* Delete `ISkyWalkingClient` interface

* Use segment protocol V2

* Forget the old api. All context apis will be overwritten.

* Add segments define

* Add some apis

* Add carrierParser

* Add SegmentContextAccessor API

* Add SampledDelegate interface

* Add thread-safe  SamplerChainBuilder

* Add SegmentContextFactory

* Add ITracingContext Interface

* Refactoring the core API for tracing context

* remove utils package

* Resolve issue #57 : Provide percentage-based sampling

* Refactor HttpClient Tracing

* Fix header carrier

* Add async exitSpan sample

* Add Task.WhenAll sample

* Refactor EntityFrameworkCore tracing

* Refactor SqlClient & CAP Tracing

* Refactor Asp.Net tracing

* Remove outdated APIs