Support tuple return args

[Arachnid]

Weiroll now supports grabbing the return value from a call and packaging the whole thing up in a bytes for future callers to use. We should support this in the planner. I think this will require some sort of explicit indication from the user that they want to do this; if we just try and set the tuple bit in the command if a return value is passed to a bytes parameter, because this will fail if the return type is itself bytes.