b4 v0.15.0 released

Version 0.15.0 of the b4 patch-management tool is out. Highlights in this
release include the b4 review workflow manager for maintainers
(covered briefly in this article), b4
dig, which can find the original mailing-list submission behind a
commit, three-way-merge support in b4 shazam, and more. See the release
notes for details.