Rename FileField to ContentField

Better aligns with attachment type metadata field name
closes #2047

Author: russcam

src/Nest/Mapping/Types/Specialized/Attachment/AttachmentAttribute.cs

@@ -7,7 +7,7 @@ public class AttachmentAttribute : ElasticsearchDocValuesPropertyAttributeBase,
 		INumberProperty IAttachmentProperty.ContentLengthField { get; set; }
 		ITextProperty IAttachmentProperty.ContentTypeField { get; set; }
 		IDateProperty IAttachmentProperty.DateField { get; set; }
-		ITextProperty IAttachmentProperty.FileField { get; set; }
+		ITextProperty IAttachmentProperty.ContentField { get; set; }
 		ITextProperty IAttachmentProperty.KeywordsField { get; set; }
 		ITextProperty IAttachmentProperty.LanguageField { get; set; }
 		ITextProperty IAttachmentProperty.NameField { get; set; }

src/Nest/Mapping/Types/Specialized/Attachment/AttachmentProperty.cs

@@ -10,7 +10,7 @@ public interface IAttachmentProperty : IDocValuesProperty
 		IDateProperty DateField { get; set; }
 		ITextProperty TitleField { get; set; }
 		ITextProperty NameField { get; set; }
-		ITextProperty FileField { get; set; }
+		ITextProperty ContentField { get; set; }
 		ITextProperty AuthorField { get; set; }
 		ITextProperty KeywordsField { get; set; }
 		ITextProperty ContentTypeField { get; set; }
@@ -48,7 +48,7 @@ public IDateProperty DateField
 			set { Dictionary["date"] = value; }
 		}
 
-		public ITextProperty FileField
+		public ITextProperty ContentField
 		{
 			get { return Dictionary["content"] as ITextProperty; }
 			set { Dictionary["content"] = value; }
@@ -86,7 +86,7 @@ public class AttachmentPropertyDescriptor<T>
 		IDateProperty IAttachmentProperty.DateField { get; set; }
 		ITextProperty IAttachmentProperty.TitleField { get; set; }
 		ITextProperty IAttachmentProperty.NameField { get; set; }
-		ITextProperty IAttachmentProperty.FileField { get; set; }
+		ITextProperty IAttachmentProperty.ContentField { get; set; }
 		ITextProperty IAttachmentProperty.AuthorField { get; set; }
 		ITextProperty IAttachmentProperty.KeywordsField { get; set; }
 		ITextProperty IAttachmentProperty.ContentTypeField { get; set; }