debian: Attribute all maintainers in changlog

debian: Attribute all maintainers in changlog

This commit further builds on historical changelog modifications,
to properly attribute all authors of the commits.

An additional d/genchangelog.sh script has been added. This allows
generation of changelog entries, internally using `debchange` (`dch`).
The script accepts an argument, which is the commit range to generate
entries for. Each commit's subject line (first line of body) is used,
along with author name and email. This information is added to the
changelog. Automatic detection (via `debchange` built-in functionality)
is used to determine whether these entries should be added to an
existing version number. If there is no UNRELEASED version, then a new
version is automatically tagged.

The new version tag will usually need to be modified, for example,
replacing an automatically generated 0.9.6-2 with 0.9.7-1.

The final release change (s/UNRELEASED/unstable/) needs to be done
manually as well, when the Git tag is actually being tagged.
`dch -r` can be useful for this particular purpose.

Signed-off-by: Valters Jansons <valter.jansons@gmail.com>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>