UDMF File format support

[HeadClot]

So - I have been talking with @andrewmcwatters about UDMF file support in the discord.
I am opening this issue as a feature request so that we have a dedicated 3D level editor for IGF.

The 1.0 spec of UDMF can be found here

[HeadClot]

A few notes -

Level editors that support the UDMF file format are as followed.

GZDoombuilder - GZDoombuilder is windows only.
SLADE - Slade is Cross platform

[andrewmcwatters]

@HeadClot I've been interested in including some sort of bsp loader as well. I wonder if these could be included as addons since they'll be much larger in scope? I wish assimp loaded them.