Add cmake module for finding msgpack
Configure cmake option to download/install msgpack
Add empty implementations of the remote API
Implement msgpack-rpc helper module

Still missing the `msgpack_rpc_dispatch` function which will be automatically
generated by a script
Add `msgpack_rpc_dispatch`/metadata generator

This adds a lua script which parses the contents of 'api.h'. After the api is
parsed into a metadata table. After that, it will generate:

- A msgpack blob for the metadata table. This msgpack object contains everything
  scripting engines need to generate their own wrappers for the remote API.
- The `msgpack_rpc_dispatch` function, which takes care of validating msgpack
  requests, converting arguments to C types and passing control to the
  appropriate 'api.h' function. The result is then serialized back to msgpack
  and returned to the client.

This approach was used because:

- It automatically modifies `msgpack_rpc_dispatch` to reflect API changes.
- Scripting engines that generate remote call wrappers using the msgpack
  metadata will also adapt automatically to API changes