Support composition of arbitrarily many CallCredentials objects

Split Node health check code into a separate package and make it use static codegen

Reduce default max message size

Updated example codegen to use grpcio-tools

Migrated python performance tests to use GA API

Removed cython client-side call tracking

Stress tests: Fix metrics-client logging

Make PHP work correctly when receiving a compressed message

PHP: add warning about shutdown function

Change the return status codes according to the doc

Merge 0.14 into master

Rename async_execution_lock --> combiner, make it use closures, unroll previous changes for idleness

This reverts commit c9d4b81d.

Changed the README file of PHP example

This ensures sync calls get cancelled after
a keyboard interrupt, as well as all calls
getting destroyed before grpc_shutdown()

Change cancelled to cancelled?

Return success status of grpc_byte_buffer_reader_init

App to manually test behavior under changing connectivity conditions

Added missing dependencies to grpc++_base