proof of concept for an openvr module in garry's mod

this code is a trainwreck

abandon hope all ye who enter here

lots of code borrowed from the following repos:
https://github.com/DrBeef/HL2-VR-Proxy
https://github.com/maxvollmer/Half-Life-VR

test lua script included which has a correct way to translate vr positions and angles to source equivalents without weird rotation problems