Exit point bug. Async kill on reload

Hello again. Two fixes now :)

:37-40 - Without it cult had no exit point, so, when gulp finished all its tasks, cult didn't exit and user had to hit ctrl+c to stop it.

:44-53 - Async killing of gulp allowing to finish its task gracefully (for example, you have an express app in your gulpfile, and if you just kill gulp and reload it right away, you will get EADDRINUSE, because gulp had no time to stop express server)