C# beta features and cleanup

Fix getpeername code on windows

Changed object keys to valid identifier names

Exposed channel target and call peer in Node wrapper

Update README.md (just a little typo)

Add user-agent for PHP

C# support for timeouts.

Fix gpr_inf_future call

Handle a race where a new call comes in post-shutdown a little better

Fix flow control

Fixes for streaming compression.

Make the server report monotonic times for deadlines

- sending of window updates is now integrated with the primary write
  path, making this far more robust
- iomgr starts up after shutdown correctly again

Renaming jwt_credentials to service_account_jwt_access_credentials.