v0.3.0: Make when-changed cross-platform

Use the cross-platform watchdog API instead of Linux-only pyinotify.
This adds support for Mac OS X, Windows, BSD, etc. Other OSes should
also be supported via watchdog's polling fallback. Enjoy!

Switch to setuptools and use install_requires

This fixes joh#17 and allows dependencies like pyinotify to be installed
automatically.

Add author_email to setup.py