Editing pass on the text for second exercise, the one that's the giant
leap for mankind. In addition to generally being terser where possible,
broke up the steps into "Mission: <foo>" headings so people can step
through the instructions one sub-mission at a time.

I think ideally this one problem would be two or even three problems,
though I'm not sure how you'd test the steps separately.
Merge pull request #24 from rvagg/ceej/problem-two-docs

make wall of text slightly less wall-ish