Implemented command line config overrides

You can set the file to read as the config file via the command line, like
this, assuming the program supports it:

  prog -config=file.cfg

You can also override indevidual key-value pairs in the config system
using this syntax:

  prog -Ckey=value

Both commands can be used together, and you can override multiple
key-value pairs at once. To use this feature of the ConfigUtility, it must
receive argc and argv as parameters to the Load() method.