Merge psh 0414

Initial merge, basic cleanup and testing.
Resolve error messages in PSH resulting from window commands and process start commands being passed together.
Small reduction in payload size via start call and arch detect diet.
Convenience method reshuffle.

TODO (though we can do this in other PRs if it'll just get this branch landed):
Create Rex::Exploitation::Powershell::Cmd for command options.
Add obfu for the command options - randomize passed flags, make IDS work harder. Add harmless flags to the mix.
Import PSH crypto routines and Ruby-size counterparts
Move more logic into Rex, look at possibility of moving the dotNet compiler to Rex as well.