fix 715 missing Seconds on DateInterval enum, string overload to specify interval on datehistogram facet

Author: Mpdreamz

src/Nest/DSL/Facets/DateHistogramFacetDescriptor.cs

@@ -109,41 +109,54 @@ public DateHistogramFacetDescriptor<T> OnField(string field)
 			Self.Field = field;
 			return this;
 		}
+
 		public DateHistogramFacetDescriptor<T> OnField(Expression<Func<T, object>> objectPath)
 		{
 			objectPath.ThrowIfNull("objectPath");
 			Self.Field = objectPath;
 			return this;
 		}
+	
+		public DateHistogramFacetDescriptor<T> Interval(string interval)
+		{
+			Self.Interval = interval;
+			return this;
+		}
+		
 		public DateHistogramFacetDescriptor<T> Interval(DateInterval interval)
 		{
 			var intervalString = interval.GetStringValue();
 			Self.Interval = intervalString;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> Interval(DateInterval interval, DateRounding dateRounding)
 		{
 			var intervalString = interval.GetStringValue();
 			var roundingString = dateRounding.GetStringValue();
 			Self.Interval = intervalString + ":" + roundingString;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> Factor(int factor)
 		{
 			Self.Factor = factor;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> Offset(string Pre = null, string Post = null)
 		{
 			Self.PreOffset = Pre;
 			Self.PostOffset = Post;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> TimeZone(string timeZone)
 		{
 			Self.TimeZone = timeZone;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> TimeZones(string Pre = null, string Post = null)
 		{
 			//elasticsearch actually sets timezone in pre_zone so reset timezone in case its set
@@ -153,42 +166,49 @@ public DateHistogramFacetDescriptor<T> TimeZones(string Pre = null, string Post
 			Self.PostZone = Post;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> KeyField(Expression<Func<T, object>> objectPath)
 		{
 			objectPath.ThrowIfNull("objectPath");
 			Self.KeyField = objectPath;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> KeyField(string keyField)
 		{
 			keyField.ThrowIfNull("keyField");
 			Self.KeyField = keyField;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> KeyScript(string keyScript)
 		{
 			keyScript.ThrowIfNull("keyScript");
 			Self.KeyScript = keyScript;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> ValueField(Expression<Func<T, object>> objectPath)
 		{
 			objectPath.ThrowIfNull("objectPath");
 			Self.ValueField = objectPath;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> ValueField(string valueField)
 		{
 			valueField.ThrowIfNull("valueField");
 			Self.ValueField = valueField;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> ValueScript(string valueScript)
 		{
 			valueScript.ThrowIfNull("valueScript");
 			Self.ValueScript = valueScript;
 			return this;
 		}
+		
 		public DateHistogramFacetDescriptor<T> Params(Func<FluentDictionary<string, object>, FluentDictionary<string, object>> paramDictionary)
 		{
 			paramDictionary.ThrowIfNull("paramDictionary");

src/Nest/DSL/Facets/DateInterval.cs

@@ -1,4 +1,4 @@
-using System;
+
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.Serialization;
@@ -11,6 +11,8 @@ namespace Nest
 	[JsonConverter(typeof(StringEnumConverter))]
 	public enum DateInterval
 	{
+		[EnumMember(Value = "second")]
+		Second, 
 		[EnumMember(Value = "minute")]
 		Minute, 
 		[EnumMember(Value = "hour")]