Refresh a lot of the copy

This includes some small and some larger(er) changes, which I'll call out specifically in a moment, but generally:

* Typos and wording (small)
* Bring some tech stuff up to date (small)
* Change a few things about the rails engineering job description (bigger)
I was thinking we should review the copy on this site on a regular basis, but it would be good to find a way to talk about the monthly gem update.  Will noodle on it.