* Baggage context part 1.
* A little cleanup.
* Return strings instead of objects. Removed default value in ctor because it generates a compiler warning about struct default constructor being used.
* Updated SDK & API projects for BaggageContext.
* Fixed broken areas, except for CorrelationContext tests.
* First round of tests and bug fixes.
* FIxed up HTTP instrumentation tests.
* Fixed up shim tests.
* More tests and improvements.
* Fixed broken test.
* Test coverage and bug fixes.
* Deterministic GetHashCode + tests.
* Added a link to the baggage api.
* Updated CHANGELOG.
* Renamed BaggageContext -> Baggage.
* CHANGELOG update.
Co-authored-by: Cijo Thomas <cithomas@microsoft.com>