Merge branch 'master' of https://github.com/grpc/grpc into codegen-paths

.gitmodules

BUILD

CONTRIBUTING.md

Makefile

binding.gyp

build.yaml

config.m4

examples/cpp/helloworld/README.md

examples/node/package.json

examples/ruby/route_guide/route_guide_client.rb

gRPC.podspec

grpc.gemspec

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

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

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

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

include/grpc++/impl/grpc_library.h

include/grpc++/impl/proto_utils.h

include/grpc++/security/auth_context.h

include/grpc++/security/auth_metadata_processor.h