Internalize ProductHeaderValue

What Haacked, PaulBetts, and Shiftkey suggested
Removed new line, doh.
More newlines

And usings :thumbsup:
Third Time's a charm
Add interface and required entities for Commit Comments.
Implement RepositoryCommentsClient
Add Repository Comments stuff to additional assemblies
Add IObservableRepositoryCommentsClient as well as an implementation
Add tests for RepositoryCommentsClient
Updated comments
Extension method for IHttpClient

To not require cancellation token
Run FixProjects
added a simple integration test and got it passing
updated impacted tests
updated convention tests
updated SimpleJson to v0.34
added hotfix to serialize base classes
enabled readonly collections support in builds
enabled readonly collection
cleanup of constants