Revert "Fixed shutdown_hook deprecation warning in IPython 2.0"

This reverts commit f40d4e1d9c3c33fca7ae55e7e75eb73774384539.
Revert "Refactored the stirling function to a class-based Function."

This reverts commit ef3a7b193e32faaa576e2eb46ad154c939aaf0b0.