version 0.22.1 released

Version 0.22.1 includes an improved moon image file for a more accurate representation of the moon. There's also better error handling for the case when glunarclock can't load or can't find the moon image file.

New in version 0.22: Selection between north and south latitude and between east and west longitude is now done graphically to reduce confusion with the sign convention. Bug fix for local Sidereal Time being displayed as negative.