#4 Height field

[Andreas Kahler]

Implement height field shape, maybe using the grid
tracing algorithm [1]

Also needs a image reading class, preferably one that
can handle 16 or 32 bit gray images

[1] MUSGRAVE, F. K. Grid Tracing: Fast Ray Tracing for
Height Fields, Technical Report YALEU/DCS/RR-639, Yale
University Department of Computer Science Research,
1988. 132