Make this project a pip-installable package

[mikepqr]

Ship the CSS file embedded in resume.py or in a data file documented in MANIFEST.in, and provide a command line option to point to custom CSS that should be embedded in the CSS file. (WIll need to verify CSS cascade behavior for this.)

(We don't want to go dependency crazy, but once this is done the additional burden of e.g. watchdog for #17 becomes small.)