Allow servers to select compression level via initial MD & overall compression cleanup

Add support for communication using existing FD (for client and server)

Polished RR policy and added policy doc preamble

Adds functions to set snd/rcv socket buffer sizes.

Factor out json serialization code from qps report.cc

This is for the same reasons as ParseJson, that is so that we can limit
the scope of the proto namespace differences between internal and
external.

added comment about host parameter format (issue 4147)

fix for issue 5548. Deprecated old classes and created subclasses.

moved core_codegen from src/cpp/... to include/grpc++/...

Check content type on the client response path

Fix refcounting algorithm for metadata

Make Metadata.Entry a class

Add interfaces for ServerAsyncReader/Writers

clang-format changes

Simplify compression interop

Remove AsyncStreaming client from python qps tests

Added python jwt_token_creds interop test

Used for non-default 1 MB UDP socket buffers.

Fix sed induced typo