Merge branch 'master' into new_scenario

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

doc/environment_variables.md

doc/epoll-polling-engine.md

doc/images/new_epoll_impl.png

doc/images/old_epoll_impl.png

gRPC-Core.podspec

grpc.gemspec

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

include/grpc++/test/server_context_test_spouse.h

include/grpc/impl/codegen/grpc_types.h

include/grpc/support/alloc.h

package.xml

src/core/ext/census/grpc_filter.c

src/core/ext/client_config/client_channel.c

src/core/ext/client_config/method_config.c