Removed some redundant calls to ReadNull and WriteNull.
CSHARP-958: Use Trie in more serializers. Simplify GeoJson serializers.
Move trie parameter from ReadBsonType to ReadName.
ported linq work over.
added support to EnumSerializer to change the offset of enums. DayOfWeekSerializer now uses EnumSerializer as a base class.
fixed rebasing issues and all tests pass.
cleanup of comments and some code.