[2.5D] Implement perspective correct 2.5D rendering.

[luciusDXL]

Another post Beta 1 feature. Implement a perspective correct 2.5D sector renderer that can support games such as Dark Forces (Jedi), Blood (Build) and potentially simpler block based engines such as Arena.

Note this applies to rendering only - the feel of the game should come from the per-game gameplay/physics implementations. The renderer should be flexible enough to accurately render the sector data from different games and engines. Finally software rendering will always be available as a fallback.