Merge pull request #2 from lagodiuk/kdtree

Using simple kd-tree for boosting speed of finding nearest object, which intersects with ray - complexity is O(log(N))
Merge pull request #3 from EarlGray/master

Added multithreaded mode + optimizations
make NCPU=<num> rungl   -- for testing
Inlined few functions, which used frequently
Refactoring + separation of logically completed pieces of code within different files
Moved canvas and color headers and sources to render sources and headers
Refactoring
Refactoring of kd-tree code
Small optimization of kd-tree building
Reduced redundant code
Working commit
Makefile fix
mt_render.c : broadcast with locked mutex
Merge remote-tracking branch 'yura/master'

Conflicts:
	makefile