Grpc ruby add support for returning metadata to the rpc server 

Add SimpleCov coverage set up for gRPC ruby

Refactoring of core security to remove the factories.

- Renamed security_context -> security_connector.
- Credentials are now responsible for creating their own connectors.

Remove usage of xray

- xray was useful during dev testing but is neither a dev or runtime dep
- its presence causes issues for libraries that handle signals themselves

Also
- updates grpc.gemspec with requirements

Fixing dependency...

- allow BadStatus to contain metadata that's populated by keyword args
- on servers, convert raised BadStatus metadata to trailers
- on clients, convert trailers to BadStatus metadata when raising BadStatus

Avoid implicit function declarations

Use TypedData_XXX instead of Data_XXX

Adding option to add a null terminator when loading a file.

Move proto files up the tree to prepare for sharing.

Grpc ruby rpc server simple signal handling

Avoid generating libs for unknown types.

Conflicts:
	src/ruby/ext/grpc/rb_grpc.c

Conflicts:
	src/ruby/ext/grpc/rb_grpc.c

Wrap ParseCommandLineFlags in InitTest

Get GRPC_TRACE tcp working again

Get run_tests.py forever mode working again

Return 1 when test_case is not supported in interop test

Registered calls

- adds signal handling to RpcServer
- ensures that very little behaviour occurs in the signal handling context
- adds #run_till_terminated that launches a server in a thread and then handles
  signals that can be used to stop it.

Updates gem dependencies, style rules