Reimplemented soft shadows. Need fast jitter...

The random function was 50% of the reason it was slow. I need to find a
faster way to generate random numbers. A precalculated list might work
well. Perhaps rand() is faster than fancy C++11 random? Needs looking
into.

12 million rays per second on my Macbook Pro (late 2013) i7 seems to be
about average. I should be careful of sudden drops in the future.
Tweaked shadow code, cleaned up john output.

Nothing special. Move along.
Tweaked the TODO.md file.
Added simple jitter to shadows.

Need to make pixel, shadow, time, focus, reflection, etc sampling
use same unique method and be clever about things. Must think about
this…