Allow other games and custom mods that use Valve220 map format

[G2Pavon]

• Custom mods:

python3 fgd_generator.py <game path>  -<mod name>

python3 fgd_generator.py /Half-Life/ -cstrike

python3 fgd_generator.py /Half-Life/ -custom_mod

if <mod name> isn't used then search in game path

• Custom models and sprites folders:

This will allow support for other games that do not have the models/ and sprites/ directory.

python3 fgd_generator.py <game path>  -<mod name> <models folder> <sprites folders>