Moved self tests to separate module
Moved self tests to separate assembly
Moved global functions to core assembly
Changed guard file to use guard-shell

The guard-rake did not pick up changes to the guard file. Also, guard
isself did not handle well when the rake job crashed. Guard would stop
looking at the files. This works better with guard-shell
Extracted tests into separate assembly
Implemented loading specs based on command line parameters
Added description of usage to readme file