-Upgrade immutable collections package
-Changed blank XML elements to be written as an empty string instead of null
-Added support for XML document type
-Changed string JValue with a null value to be written as null instead of empty string
-Fixed StringEnumConverter thread safety
-Fixed using FloatParseHandling.Decimal with XmlNodeConverter
-Fixed using DateParseHandling.DateTimeOffset with XmlNodeConverter
-Fixed build