XML Constructors v1 & Json changes

- Changed JsonSaveOption to Flags
- Added NoEncoding and RemoveNulls JsonSaveOption flags
- Add JsonValue constructors for provided Json types
- Add XElement constructors for provided XML types
- Add element / attribute constructors for provided XML types

Notes:
XML Heterogeneous type constructors not tested at all
Not sure on naming parameters - might not work properly if an XML node has attributes and elements with the same names - have not tested this yet
Culture - not sure what to do with this for the XML constructors
Still work in progress.