Merge pull request #4653 from murgatroid99/release-0_12_master_merge

.rspec

BUILD

Gemfile

Makefile

Rakefile

binding.gyp

build.yaml

gRPC.podspec

grpc.gemspec

include/grpc++/client_context.h

include/grpc++/security/credentials.h

include/grpc/grpc.h

package.json

src/core/surface/call.c

src/core/surface/validate_metadata.c

src/core/transport/chttp2/bin_encoder.c

src/core/transport/chttp2/bin_encoder.h

src/core/transport/chttp2/hpack_encoder.c

src/core/transport/chttp2/hpack_parser.c

src/core/transport/metadata.c