Util: Added script to semantically diff two config.ini files

Util: Added script to semantically diff two config.ini files

This script (util/diff_config.pl) takes two config.ini files and compares them.
It highlights value changes, as well as displaying which parts are unique to
a specific config.ini file. This is useful when trying to replicate an earlier
experiment and when trying to make small changes to an existing configuration.