The current way of creating the changelog file for the package
is based on reading the entire history of the git repository and
turns that information into a changelog. The downside of this
approach is that any change in the code that creates this changelog
information will impact older entries and could cause a conflict
on the changes file of the released package. This usually leads
to declined package submissions and blocks us in fixing bugs
in the changelog generator. This commit changes the process in
a way that only changes related to the oldest entry of a reference
changelog file compared to the current branch are taken into
account. This Fixes#979
