added command line arguments
added cos_theta() and abs_cos_theta() to util.hpp
made gray.exe the default target in Makefile
added cosine term to light transport equation in PathIntegrator
fresnel stuff
fixed bug in abs_cos_theta()
added scene for testing fresnel
Added sin_theta(w) and sin2_theta(w).
Added SpecularTransmission and Glass material (which does not work)
some fixes in path integrator
show progress (scanline number) in console
test1.scene had colors that were picked from gamma space, converted to linear space
catch all exceptions in main loop
checkers texture draft
Rendering now works in blocks
simple multi-threading support
nicer test scene
Merge branch 'multicore'