Awood/systemd

This branch gets thumbslug working under systemd.

Additionally:
- fixes the thumbslug spec tests so that they run again
- uses jpackge_script macro to generate a nice wrapper script for us
- updates to the latest version of Buildr
- modifies thumbslug to take a single argument: the name of the conf file to use if not /etc/thumbslug/thumbslug.conf
- adds some documentation on how to perform an end-to-end test