Some improvements to cb-hotcorners

I made some changes/improvements to cb-hotcorners:

 * Use [XDG-Basedir](http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html) spec to find the config directory instead of assmuing
 the default one.
 * Use [docopt](http://docopt.org/) for argument handling.
 * Made the "bounce" configurable in the configuration file.
 * Some minor code improvements.
 * [PEP8](http://www.python.org/dev/peps/pep-0008/) compliance.