Merge branch 'master' of github.com:grpc/grpc into codegen_lib

CONTRIBUTING.md

Makefile

build.yaml

composer.json

examples/php/composer.json

examples/php/greeter_client.php

examples/php/route_guide/route_guide_client.php

include/grpc++/impl/codegen/completion_queue.h

include/grpc++/impl/codegen/server_context.h

package.xml

setup.py

src/core/channel/client_channel.c

src/core/channel/subchannel_call_holder.c

src/core/client_config/client_config.c

src/core/client_config/lb_policies/pick_first.c

src/core/client_config/resolvers/dns_resolver.c

src/core/client_config/subchannel.c

src/core/iomgr/iocp_windows.c

src/core/iomgr/iocp_windows.h

src/core/iomgr/resolve_address.h