New Item Attribute API, and some NBT API changes.

[ATTRIBUTES]
* NEW: New API to manipulate attributes on items (for now). This API 
  also permits using custom attributes with custom UUIDs.

[NBT]
* NEW: The NBT API is now a component.
* NEW: NBTCompound and NBTList are now public classes.
* NEW: NBTList and NBTCompound: get() methods can now take default values.
* NEW: NBTList and NBTCompound can now be created without an associated
  item.
* NEW: NBTList and NBTCompound can now be built even if the associated
  value is not a list or a compound (or does not exist), and the value
  will be overwritten if anything is added to the tag.
* NEW: NBTList.filter() is returns a new iterator, that iterates only
  over values that can be coerced to the given type.
* NEW: Upon failure, NBT classes now throw NBTExceptions instead of
  generic RuntimeExceptions.
* NEW: Added missing Javadoc.
* BUG: Boxed native types are now correctly supported.
* BUG: Fixed writing NBT data.
* BUG: Fixed handling on some null values.

[REFLECTION]
* NEW: Reflection.instanciate() can now access non-accessible 
  constructors.

Author: prokopyl

src/main/java/fr/zcraft/zlib/components/attributes/Attribute.java

@@ -0,0 +1,252 @@
+/*
+ * Copyright or © or Copr. ZLib contributors (2015 - 2016)
+ *
+ * This software is governed by the CeCILL-B license under French law and
+ * abiding by the rules of distribution of free software.  You can  use,
+ * modify and/ or redistribute the software under the terms of the CeCILL-B
+ * license as circulated by CEA, CNRS and INRIA at the following URL
+ * "http://www.cecill.info".
+ *
+ * As a counterpart to the access to the source code and  rights to copy,
+ * modify and redistribute granted by the license, users are provided only
+ * with a limited warranty  and the software's author,  the holder of the
+ * economic rights,  and the successive licensors  have only  limited
+ * liability.
+ *
+ * In this respect, the user's attention is drawn to the risks associated
+ * with loading,  using,  modifying and/or developing or reproducing the
+ * software by the user in light of its specific status of free software,
+ * that may mean  that it is complicated to manipulate,  and  that  also
+ * therefore means  that it is reserved for developers  and  experienced
+ * professionals having in-depth computer knowledge. Users are therefore
+ * encouraged to load and test the software's suitability as regards their
+ * requirements in conditions enabling the security of their systems and/or
+ * data to be ensured and,  more generally, to use and operate it in the
+ * same conditions as regards security.
+ *
+ * The fact that you are presently reading this means that you have had
+ * knowledge of the CeCILL-B license and that you accept its terms.
+ */
+
+package fr.zcraft.zlib.components.attributes;
+
+import fr.zcraft.zlib.components.nbt.NBT;
+import fr.zcraft.zlib.components.nbt.NBTCompound;
+import java.util.UUID;
+
+/**
+ * This class represents an item attribute.
+ */
+public class Attribute 
+{
+    NBTCompound nbt;
+    
+    /**
+     * Creates a new empty attribute, not linked to any item.
+     */
+    public Attribute()
+    {
+        this(new NBTCompound());
+    }
+    
+    Attribute(NBTCompound nbt)
+    {
+        this.nbt = nbt;
+    }
+    
+    /**
+     * @return the name of this attribute's modifier. It can be any string.
+     */
+    public final String getName()
+    {
+        return nbt.get("Name", null);
+    }
+    
+    /**
+     * Sets the name of this attribute's modifier.
+     * This name can be set to any string value.
+     * @param name The name.
+     */
+    public final void setName(String name)
+    {
+        nbt.put("Name", name);
+    }
+    
+    /**
+     * Returns the name of the Attribute this Modifier is to act upon.
+     * Example: generic.attackDamage
+     * See http://minecraft.gamepedia.com/Attribute#Attributes for more information.
+     * @return the name of the Attribute this Modifier is to act upon.
+     */
+    public final String getAttributeName()
+    {
+        return nbt.get("AttributeName", null);
+    }
+    
+    /**
+     * Sets the name of the Attribute this Modifier is to act upon.
+     * @param attributeName The attribute name.
+     */
+    public final void setAttributeName(String attributeName)
+    {
+        nbt.put("AttributeName", attributeName);
+    }
+    
+    /**
+     * Returns the most significant bytes of this modifier's UUID.
+     * @return the most significant bytes of this modifier's UUID.
+     */
+    public final Long getUUIDMost()
+    {
+        return nbt.get("UUIDMost", null);
+    }
+    
+    /**
+     * Sets the most significant bytes of this modifier's UUID.
+     * @param uuidMost the bytes.
+     */
+    public final void setUUIDMost(long uuidMost)
+    {
+        nbt.put("UUIDMost", uuidMost);
+    }
+    
+    /**
+     * Returns the least significant bytes of this modifier's UUID.
+     * @return the least significant bytes of this modifier's UUID.
+     */
+    public final Long getUUIDLeast()
+    {
+        return nbt.get("UUIDLeast", null);
+    }
+    
+    /**
+     * Sets the least significant bytes of this modifier's UUID.
+     * @param uuidLeast the bytes.
+     */
+    public final void setUUIDLeast(long uuidLeast)
+    {
+        nbt.put("UUIDLeast", uuidLeast);
+    }
+    
+    /**
+     * Returns this modifier's UUID.
+     * @return this modifier's UUID.
+     */
+    public final UUID getUUID()
+    {
+        Long uuidMost = getUUIDMost();
+        Long uuidLeast = getUUIDLeast();
+        
+        if(uuidMost == null || uuidLeast == null)
+            return null;
+        
+        return new UUID(uuidMost, uuidLeast);
+    }
+    
+    /**
+     * Sets this modifier's UUID.
+     * @param uuid the new modifier's UUID.
+     */
+    public final void setUUID(UUID uuid)
+    {
+        setUUIDMost(uuid.getMostSignificantBits());
+        setUUIDLeast(uuid.getLeastSignificantBits());
+    }
+    
+    /**
+     * Returns the Minecraft NBT/JSON string representation of this attribute.
+     * See {@link fr.zcraft.zlib.tools.nbt.NBT#toNBTJSONString(java.lang.Object) } for more information.
+     * @return the Minecraft NBT/JSON string representation of this attribute.
+     */
+    @Override
+    public String toString()
+    {
+        return NBT.toNBTJSONString(nbt);
+    }
+    
+    /**
+     * Returns the underlying NBT compound of this attribute.
+     * @return the underlying NBT compound of this attribute.
+     */
+    public final NBTCompound getNBTCompound()
+    {
+        return nbt;
+    }
+    
+    /**
+     * Returns the custom data payload associated to this attribute.
+     * This enabled plugins to put custom Attributes (and data) to any item.<br>
+     * The data payload is actually stored as the name of the attribute's modifier, which is not used by the game.<br>
+     * However, as the custom data shows an empty line (per slot in 1.9+ !) in 
+     * the item's tooltip in the client, you may want to hide item attributes.
+     * @return the custom data payload associated to this attribute.
+     */
+    public final String getCustomData()
+    {
+        return getName();
+    }
+    
+    /**
+     * Sets the custom data payload associated to this attribute.
+     * See {@link #getCustomData() } for additional information.
+     * @param data the new data.
+     */
+    public final void setCustomData(String data)
+    {
+        setName(data);
+    }
+    
+    /**
+     * Returns this modifier's operation.
+     * @return this modifier's operation.
+     */
+    public final AttributeOperation getOperation()
+    {
+        return AttributeOperation.fromCode(nbt.get("Operation", 0));
+    }
+    
+    /**
+     * Sets this modifier's operation.
+     * @param operation The new operation value.
+     */
+    public final void setOperation(AttributeOperation operation)
+    {
+        nbt.put("Operation", operation.getCode());
+    }
+    
+    /**
+     * Returns the slot for which this modfier applies.
+     * @return the slot for which this modfier applies.
+     */
+    public final String getSlotName()
+    {
+        return nbt.get("Slot", null);
+    }
+    
+    /**
+     * Sets the slot for which this modfier applies.
+     * @param slotName 
+     */
+    public final void setSlotName(String slotName)
+    {
+        nbt.put("Slot", slotName);
+    }
+    
+    /**
+     * Returns the amount of the modification.
+     * @return the amount of the modification.
+     */
+    public final double getAmount()
+    {
+        return nbt.get("Amount", 0.0);
+    }
+    
+    /**
+     * Sets the amount of the modification.
+     * @param amount 
+     */
+    public final void setAmount(double amount)
+    {
+        nbt.put("Amount", amount);
+    }
+}

src/main/java/fr/zcraft/zlib/components/attributes/AttributeOperation.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright or © or Copr. ZLib contributors (2015 - 2016)
+ *
+ * This software is governed by the CeCILL-B license under French law and
+ * abiding by the rules of distribution of free software.  You can  use,
+ * modify and/ or redistribute the software under the terms of the CeCILL-B
+ * license as circulated by CEA, CNRS and INRIA at the following URL
+ * "http://www.cecill.info".
+ *
+ * As a counterpart to the access to the source code and  rights to copy,
+ * modify and redistribute granted by the license, users are provided only
+ * with a limited warranty  and the software's author,  the holder of the
+ * economic rights,  and the successive licensors  have only  limited
+ * liability.
+ *
+ * In this respect, the user's attention is drawn to the risks associated
+ * with loading,  using,  modifying and/or developing or reproducing the
+ * software by the user in light of its specific status of free software,
+ * that may mean  that it is complicated to manipulate,  and  that  also
+ * therefore means  that it is reserved for developers  and  experienced
+ * professionals having in-depth computer knowledge. Users are therefore
+ * encouraged to load and test the software's suitability as regards their
+ * requirements in conditions enabling the security of their systems and/or
+ * data to be ensured and,  more generally, to use and operate it in the
+ * same conditions as regards security.
+ *
+ * The fact that you are presently reading this means that you have had
+ * knowledge of the CeCILL-B license and that you accept its terms.
+ */
+
+package fr.zcraft.zlib.components.attributes;
+
+/**
+ * This enum represents the possible values for an item attribute operation.
+ */
+public enum AttributeOperation 
+{
+    /**
+     * Operation 0: Additive. Adds all of the modifiers' amounts to the current value of the attribute.
+     */
+    ADDITIVE(0),
+    /**
+     * Operation 1: Multiplicative. Multiplies the current value of the attribute by (1 + x), where x is the sum of the modifiers' amounts.
+     */
+    MULTIPLY(1),
+    /**
+     * Operation 2: Multiplicative. For every modifier, multiplies the current value of the attribute by (1 + x), where x is the amount of the particular modifier. 
+     * Functions the same as Operation 1 if there is only a single modifier with operation 1 or 2. 
+     * However, for multiple modifiers it will multiply the modifiers rather than adding them.
+     */
+    MULTIPLY_ALL(2);
+    
+    private final int code;
+    private AttributeOperation(int code)
+    {
+        this.code = code;
+    }
+    
+    /**
+     * 
+     * @return the operation's code.
+     */
+    public int getCode()
+    {
+        return code;
+    }
+    
+    @Override
+    public String toString()
+    {
+        return String.valueOf(code);
+    }
+    
+    /**
+     * Gets an AttributeOperation from its code.
+     * @param code The attribute code.
+     * @return the corresponding attribute operation.
+     * @throws IllegalArgumentException if the code is invalid.
+     */
+    static public AttributeOperation fromCode(int code) throws IllegalArgumentException
+    {
+        for(AttributeOperation operation : values())
+        {
+            if(operation.code == code)
+                return operation;
+        }
+        
+        throw new IllegalArgumentException("Illegal Attribute operation code : " + code);
+    }
+}