normal-map[css]: Add normal-map CPU shader function.

Implementation based off GLSL example by mattdesl:
https://github.com/mattdesl/lwjgl-basics/wiki/ShaderLesson6
normal-map[css]: Add missing texel position transformation.

Rename some variables for clarity.
normal-map[css]: Add drawOutput() function.

Simplify canvas creation. Add default light variables.
normal-map[css]: Add mouse control of light position.