added bash script for caching of dfree results
/usr/bin/greyhole-dfree is now a shell script that will return a cached value. The cache will be refreshed every 15s using the old script that is now in /usr/share/greyhole/greyhole-dfree.php
Fixes GH-111
Modified sample greyhole.conf, because having comments at the end of a line is not supported by the parser.