This removes the old NEWS file and splits up all the release notes into

ReST files. These can later be shown directly on the Review Board

website, instead of having to go through the NEWS files on

downloads.reviewboard.org. This will also make it easier for us to link

to Djblets release notes in other docs.
Each of these files were copy/pasted from their NEWS sections, with some

macros and regexes used to transform them into the proper format. I also

went through some of them and fixed up styling, and added appropriate

ReST markup where needed.

Built the docs. Didn't see any errors.
Skimmed through each doc page and didn't see anything glaringly wrong.
I don't expect a lot of review into each individual release note file. There's

a lot of them, and they're basically the same content as what we shipped, but

with some backticks and domains sprinkled here and there.