Shared subchannel sketch

BUILD

Makefile

binding.gyp

build.yaml

gRPC.podspec

src/core/client_config/subchannel.c

src/core/client_config/subchannel_index.c

src/core/client_config/subchannel_index.h

src/core/surface/init.c

src/python/grpcio/grpc_core_dependencies.py

tools/doxygen/Doxyfile.core.internal

tools/run_tests/sources_and_headers.json

vsprojects/vcxproj/grpc/grpc.vcxproj

vsprojects/vcxproj/grpc/grpc.vcxproj.filters

vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj

...jects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters