Project Bedrock transports

[Rick-Anderson]

See https://github.com/aspnet/KestrelHttpServer/issues/1980 and Bedrock update
Document the lower layers.
The transports

[davidfowl]

I want to be careful how we document this, it isn't a part of SignalR anymore it was pushed even down the stack.

[Rick-Anderson]

Closing.