Append immediate execution to start action

This PR improves **Start** action for immediate execution and append **Schedule** action to avoid it.

Ref. threefunkymonkeys/crocodile#3
Let's swtich the alias methods. Keep the original `one_run_only` as a method and add the alias for `dismiss?`.
This way we respect the original interface and add some syntax sugar.
I think that's the only thing left, then I'll merge it and release a new version.

Thank you @lguardiola!!!