Chapter Prose

First draft of the chapter prose, in rst form for now. I'm requesting PR to have someone look at the prose. I've also included an svg diagram, but you'll have to pull the repository to see it. I don't think it's viewable within github...

If you want to pull this, this is the 'chapter' branch from https://github.com/malini/500lines
You should 'cd test_repo' before initializing the repo here.