Implemented Ward's operator
Tweaked ldmax, rendered images at various scene light intensities.

Distressingly, individual channels seemed to be pegged at
intensities as low as 50.
Implemented Reinhard operator
Implemented extra allowing for different key mappings

Use Prelude functions (const foo) or (!! bar) i.e. indexing function
with reinhardTR' to use a constant key value or sample a pixel in the
image, respectively.
Updated main function for checkpoint 7
Final tweaks for distribution

NabRay.hs defines module Main.
All dependencies accounted for in nabray.cabal
README.md updated with build instructions.
Distribution package added to source control.