Plotting functions, eye model improvements

[gkaguirre]

• Added functions for schematic and rendered eye illustrations
• Cleaned up the projection matrices with some advice from Kostas Danilidis
• Tweaked the eye model
• Improved the intersection of the ray with the nodal point in the virtual image function

I've come to the realization that the ray tracing must be performed in 3D, and not in independent 2D planes. Will work on this in the next branch.