Merge branch 'master' into debug_qps_stream

CONTRIBUTING.md

INSTALL.md

examples/README.md

examples/cpp/README.md

examples/php/README.md

examples/python/route_guide/route_guide_server.py

setup.py

src/core/channel/client_channel.c

src/core/channel/subchannel_call_holder.c

src/core/iomgr/timer_heap.c

src/cpp/README.md

src/node/README.md

src/node/src/client.js

src/php/README.md

src/python/grpcio/README.rst

src/python/grpcio/commands.py

...thon/grpcio/grpc/_cython/_cygrpc/completion_queue.pyx.pxi

src/python/grpcio/precompiled.py

src/python/grpcio/tests/_runner.py

src/ruby/.rubocop.yml