Media Type Handler Updates

Add MediaTypeHandlerBase that allows for separation of read/write wire
format, object graph to/from wire format, custom link management for root
items and collections.
cleanup and merge HalJson into JsonNet, removed old HalJson projects
Xml and Json.Net handlers use this new base.
Renamed the existing JsonMediaTypeHandler to
JsonMediaTypeHandlerWithDeepLinks
Cleaned up and organized the Solution file
Added MediaTypeHandler performance test harness
Fix mixed JsonNet versions + Mono build.
Merge pull request #76 from EddieGarmon/feature-MTH

Media Type Handler Updates