Perform 'blurb split' for 3.3.

[larryhastings]

No description provided.

[brettcannon]

Quick perusal LGTM.

[ned-deily]

See comments on #2719 for master, e.g. breaking doc builds of Doc/whatsnew/changelog.rst. But I wonder whether we should even bother doing this for 3.3 since it is so close to end-of-life and the Doc/Makefile for 3.3 is much older, e.g. it doesn't use venv or pip to build docs but rather downloads build tools using svn! At least, let's hold off on 3.3 until I've had a chance to play with it a bit more.

[larryhastings]

I hear and obey--I'll hold off.

If any of the cherry-picks back into 3.3 have Misc/NEWS.d blurb entries, I guess you'll have two choices:

1. Manually merge them into Misc/NEWS, or
2. Run blurb split and blurb merge yourself as part of the release process, without checking in any of the intermediary files, just to regenerate Misc/NEWS. Then check your changes to Misc/NEWS in.
   This will have the happy side-effect of also updating your Misc/NEWS to the modern aesthetics (e.g. bpo-, section name "macOS").

I think 2. is the way to go, personally; it seems like a very sensible approach to handling the end-of-life 3.3 branch overall. Misc/NEWS will remain where it is so it won't affect the Doc build process.

[ned-deily]

Yeah, I think running blurb split and blurb merge manually during the release tagging makes sense to get the updated references. I'll plan to do that.