Mars heightmap and fractals

This update adds the mars heightmap and roughness map as well as terrain code which has been worked on alongside @s20dan.

The roughness data was taken from this website http://www.planetary.brown.edu/rough/index.html which contains data accompanying an excellent series of papers by Kreslavsky and Head (2002, 2000, 1999). 

The height data was processed from the Mars Orbital Laser Altimetry data.

**Review**:
This pull request is very straightforward to review. Nothing much in the terrain code can affect much else as, regardless of how complicated it is, at the end of the day, it only outputs height above zero and colours which are clamped before being sent to GPU. If oddities are present they will just manifest as interesting bumps or colours (@s20dan's has already looked through an early version of the colour code). This leaves the simple terrain loading code, which loads a few variables followed by a binary blob like for all heightmaps, and the surrounding misc code.

* Two new files are added in the src/terrain folder. The MSVC 2008 project has been updated.

* It might be an idea to not merge it until the a24 freeze on Friday as I might find time to do another pass over the colour or terrain code, which will be trivial to verify as ok. Or I can do another PR, I guess.

* If anyone feels like adding in stations to mark significant places feel free to do so, as I'm unlikely to get time to before a24 freeze. There is a map here http://www.mapsharing.org/MS-maps/map-pages-planets-map/images-planets-map/1-planet-mars-map.jpg.