LP#2051874: new tool to help create release notes

LP#2051874: new tool to help create release notes

extract_release_notes_from_commits.pl, found in docs/tools in the
source tree, looks for release note, author, committer,
reviewer, and sponsor information from a stream of commits
in the branch specified by the --current-branch option
from the commit that is the common ancestor of the branch
specified by --prev-release-branch, which will normally be
a tag branch for a previous release.

The output (sent to standard output) is AsciiDoc suitable for
pasting in release notes listing the short release notes (as
entered in Release-note tags in the commit messages), the
contributors (defined as patch authors, committers, and reviewers
from the Signed-off-by tags in the commit messages) and sponsors
(from the Sponsored-by tags in the commit messages).

The output of this script should be proofread before publishing
release notes.

Usage:

--prev-release-branch=<Git commit reference>
    Branch identifying the previous release to compare
    against. Would be something like origin/tags/rel_3_12_0
--current-branch=<Git commit reference>
    Branch to look for commits on. If not specified, defaults
    to "HEAD"
--help
    Print this help message

To test
-------
[1] Ensure that your Git checkout is up to date.
[2] Run the tool and compare its output with what you would
    expect from a manual inspection of the Git commit log.

Release-note: New development tool to help prepare release notes using information from Git commits.

Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>
Signed-off-by: Andrea Buntz Neiman <abneiman@equinoxOLI.org>
Signed-off-by: Jane Sandberg <sandbergja@gmail.com>