Add docs

[ixjlyons]

Docs would be very useful for demonstrating functionality provided.

• Simple option: write an example script per function, put the generated figures in master, then put them in the README. I'm not a huge fan of this idea, but it is easy.
• Slightly less simple option: write example scripts, put generated figures in gh-pages branch, and generate a site either manually or with a commit hook or something.
• Sphinx docs on readthedocs: write some actual docs with example scripts, use mpl's plot directive to generate plots. A bit painful to set up but shouldn't be too bad -- just seems overkill if this doesn't go anywhere.