Allow ini file to be specified as a cmdline param

The full path of the ini file can be specified as a commandline
parameter.
- If an ini file is specified and is valid it will be used
- If an ini file is specified and is not valid the program will probably
fail silently (YMMV)
- If an ini file is not specified then the program will attempt to use a
file called "mappings.ini" in the same directory as the script/exe