added run_tests and test for common.cpp

added Test for common.cpp
add obj loader (geometry only)

basic loading of triangles
added mtl loader

mtl loader tests, and working

renamed mlt_loader to mtl_loader
obj loader loads mlt materials

obj loader uses mtl

simplified loaders
flipped image render and pathtrace along both diffuse and spec at the same time
bugfixed perturb (common.h) and expanded tests a bit