contrib: import the relnotes script from the release-tools repo...
contrib: import the relnotes script from the release-tools repo
I figure this makes more sense to keep in the main repo, as it's a
guide of sorts on how to use the releasenotes extension in the
presence of commits that don't get relnotes annotations.
Ported to Python 3, cleaned up some logic in a few places, but for the
most part it's what we've been using for years.
Differential Revision:
https://phab.mercurial-scm.org/D4291