Merge branch 'direct-calls' into buffer_pools_for_realsies

.gitmodules

BUILD

CMakeLists.txt

Makefile

build.yaml

composer.json

doc/PROTOCOL-HTTP2.md

doc/environment_variables.md

examples/ruby/route_guide/route_guide_client.rb

examples/ruby/route_guide/route_guide_server.rb

grpc.gemspec

include/grpc++/ext/reflection.pb.h

include/grpc/impl/codegen/grpc_types.h

src/compiler/php_generator.cc

src/compiler/php_generator.h

src/compiler/php_generator_helpers.h

src/compiler/php_plugin.cc

src/compiler/python_generator.cc

src/core/ext/client_config/subchannel.c

src/core/ext/lb_policy/grpclb/grpclb.c