Initial file for simulating the lens configuration.

Based on a drawing by http://www.frantzmartinache.com/blog/?p=84, which
uses matplotlib to draw some rays and lenses, adapting it for my
purposes.
This initial version changes some variable names and cleans up the code.
The drawing is crooked, but working.

Now drawing head-on and side view, both with correct sizes.
The rays are drawn wrongly (i.e. crooked), but at least they're drawn...