Revert "Revert "Metadata handling rewrite""

.gitignore

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.def

grpc.gemspec

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

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

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

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

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

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

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

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

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

include/grpc/compression.h