Add Quake II MD2 model format

[jdjakub]

I've been working with this format recently and saw it was missing, so I plugged the gap! I've followed the syle guide as far as I can tell, though being new to Kaitai I don't know what I should do with the overfull conditional expression lines.

You can find examples as tris.md2 under http://tastyspleen.net/~quake2/baseq2/players/. A nice, simple example is crate/tris.md2 which is just standard box geometry repeated across all frames.

[jdjakub]

I've incorporated your suggested changes.

[jdjakub]

Thanks for your detailed dive into all the issues. I've incorporated your changes. Back to you :)

[jdjakub]

Hello! I think this is mergeable now.