debian: Rework historical changelog

debian: Rework historical changelog

Rewriting history is generally considered a "not-so-good" thing,
however here the historical data does not align with best practises
and therefore it is beneficial to provide a better example going
forward.

There is only one initial release. Everything following that should
list some kind of release notes or changelog, or at the very least
just say something along the lines of "New version" rather than
"Initial release".

In this commit, the Git history is used for this task,
filtering out "Makefile" changes as to retain only changes
that are visible to users, excluding building tooling.

For Debian packages, upon release, the target distribution should be
updated to "unstable" (or "experimental" if preferred for any reason)
when a release is finalized. During development, an invalid
distribution name is expected to be there for tracking unreleased
changes. That is why "UNRELEASED" is the standard way of specifying
ongoing development, being an invalid distribution name itself.

The "(Closes: #XXXXXX)" tag is intended for linking to Debian bug
tracker, such as linking to the initial Intent to Package ticket,
or later update/bugfix tickets. There does not appear to be a bug
tracker in use for this task here, and the XXXXXX bug ticket number
does not take you anywhere. It's therefore better to just remove it.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>