Changelog overhaul...again

[bitprophet]

This is just a stand-in issue for a big ol' change I just made to the changelog. tl;dr the source format is almost identical to before, but now it "compiles" to broken-down-by-release HTML which should be vastly easier to read.

Cake status: had and eaten. 🍰

Will post comment w/ link to the detailed blog post I am polishing, when this is 100% pushed.

[bitprophet]

Blog post: http://bitprophet.org/blog/2013/09/14/a-better-changelog/

[bitprophet]

Backported to 1.7 only for now. Probably not super hard to update 1.6 as well, but - part of the point here is folks no longer need to visit "old" changelogs to get a useful view. The latest one will always be accurate.

1.7 had like two commits less than master, so...yea. Why not.