Merged from master

.gitignore

BUILD

Makefile

Rakefile

binding.gyp

build.yaml

doc/statuscodes.md

gRPC.podspec

grpc.def

grpc.gemspec

include/grpc/grpc_security.h

include/grpc/grpc_zookeeper.h

include/grpc/impl/codegen/port_platform.h

package.json

setup.py

src/core/census/placeholders.c

src/core/security/google_default_credentials.c

src/core/security/json_token.c

src/core/security/security_connector.c

src/core/security/security_connector.h