Execution

Just for feedback
Well, I do want to provide the `args` method. But it should probably be a val in the MaestroConfig body rather than a parameter.

I don't want the users calling `getArgs` many times: it's a little inconvienent, and `getArgs` is de-serializing an args string and recreating the Args with every invocation. Probably not really a problem, but I wasn't comfortable with it.