RPC framework and message specification for Rigetti QCS

 Asynchronous RPC client-server framework and message
 specification for Rigetti Quantum Cloud Services (QCS).
 Implements an efficient transport protocol by using
 ZeroMQ (ZMQ) sockets and MessagePack (msgpack) serialization.
 Not intended to be a full-featured replacement for other
 frameworks like gRPC or Apache Thrift.