Center the model at the origin.
It might be better to make this an option, and/or center it at the player start position, but this makes it easier to import the obj into other apps.
Merge branch 'master' of https://github.com/jminor/omgifol

Conflicts:
	demo/wad2obj.py
Fixed formatting of the help string.
Renamed some options to make more sense.
Added an option to center the output geometry.
Added an option to list the available maps in the source wad.
Added an option to specify the output directory to write to.