After a bit more thinking, we will create new SDK packages for each
of the languages we wish to support writing resource providers in.
This is where the RPC goo will live, so I have created a new sdk/
directory, moved the Protobuf/gRPC definitions underneath sdk/proto/,
and put the generated code into sdk/go/ and sdk/js/.
This change moves the RPC definitions to the pkg/murpc package,
underneath the proto folder. This is to ensure that the resulting
Protobufs get a good package name "murpc" that is unique within the
overall toolchain. It also includes a `generate.sh` script that
can be used to manually regenerate client/server code. Finally,
we are actually checking in the generated files underneath pkg/murpc.
