Fix some visibility issues to comply with the docs

Author: FagnerMartinsBrack

src/main/java/org/jscookie/ConverterStrategy.java

@@ -1,6 +1,6 @@
 package org.jscookie;
 
-interface ConverterStrategy {
+public interface ConverterStrategy {
 	/**
 	 * Apply the decoding strategy of a cookie. The return will be used as the cookie value
 	 * 

src/main/java/org/jscookie/CookieParseException.java

@@ -1,7 +1,9 @@
 package org.jscookie;
 
-public class CookieParseException extends Exception  {
+public final class CookieParseException extends Exception  {
 	private static final long serialVersionUID = 1;
+	@SuppressWarnings( "unused" )
+	private CookieParseException() {}
 	CookieParseException( Throwable cause ) {
 		super( cause );
 	}

src/main/java/org/jscookie/CookieSerializationException.java

@@ -2,6 +2,8 @@
 
 public class CookieSerializationException extends Exception {
 	private static final long serialVersionUID = 1;
+	@SuppressWarnings( "unused" )
+	private CookieSerializationException() {}
 	CookieSerializationException( Throwable cause ) {
 		super( cause );
 	}

src/test/java/org/jscookie/test/unit/CookiesConverterTest.java

@@ -5,6 +5,7 @@
 import javax.script.ScriptException;
 
 import org.jscookie.ConverterException;
+import org.jscookie.ConverterStrategy;
 import org.jscookie.Cookies;
 import org.jscookie.test.unit.utils.BaseTest;
 import org.junit.Assert;
@@ -51,4 +52,16 @@ public String convert( String value, String name ) throws ConverterException {
 		expected = "京";
 		Assert.assertEquals( expected, actual );
 	}
+
+	@Test
+	public void should_be_able_to_create_a_custom_strategy() {
+		this.cookies.withConverter( new CustomConverter() );
+	}
+
+	private class CustomConverter implements ConverterStrategy {
+		@Override
+		public String convert( String value, String name ) throws ConverterException {
+			return value;
+		}
+	}
 }