Ability to choose game data folder

[DanKorell]

On Windows, v0.8.0, the dethrace files need to extracted to where the Carmageddon executable is located. If you then have the Splat Pack or the demos, they each have their own executables, so you need a separate copy of the dethrace files extracted to each one, so all are treated as separate instances.

Would it be possible to have a flag to point dethrace to the folder to use so that you only need one copy of the dethrace files?