Adding NPN support if ALPN support is not available.

fix json_rewrite_test CRLF handling

Corrects the cancel_after_first_response behaviour

- introduces a #wait method on the call operation view
- invokes #wait on a Notifier that is created for all operations
- ensures the Notifier is invoked if necessary whenever a client request
  completes
- updates the interop_test to use op.wait before checking if the call
  was cancelled.

Re-enabled warnings in the gRPC podspec

Adding clang packages for msan/tsan/asan testing.

Add package.xml file for pecl extension

prevent leaking gpr_slice in windows on_read()

Added missing but included headers to build.json

- ALPN may not be available:
  - because OpenSSL does not support it.
  - because one of the peers does not support it.
- Tested manually end to end by forcing TSI_OPENSSL_ALPN_SUPPORT to 0.
  Also tested if only one of the peers supports ALPN.

Introduced compression levels as an abstraction for the actual algorithm

Disallow started request writers on GRPCCall init

Prints test names as ruby tests run

make sure docker image is up-to-date before each build

Document core behavior w.r.t. argument lifetimes

Also clean up some excess whitespace and make some notes about ownership.

Support sending and showing received metadata in grpc_cli

New core shutdown API

Link to official protobuf podspec in the README

It was still linking to my pull request's podspec.

temporary hotfix before backup poller removal is done

Transforming gRPC.podspec to use build.json instead of globbing.

Initial progress on ruby shutdown api migration