Run Length Encoding

I have finished implementing the run length encoding optimisation. For the skull, render times have been reduced from around 2 seconds to 1.3 seconds. The run length encoding gives the best improvement on images such as the skull where there is a lot of empty space that can be skipped. When most of the volume is only partially transparent there is less improvement.

Since I now have a decent interactive framerate even on my single core PC I will probably look at tweaking the image warp to get it correct before moving onto multithreading.