introduce changelog

[kadhonn]

we will need a changelog documenting changes between releases

we will need at least two changelogs, one for added features and one for changes needed for the deployment

the question is how we should do this? we could

• force everyone to add their changes directly to the changelog file
• force everyone to add their changes into their commit message and scrape them at the end of a release to create the changelog
• force everyone to create a new subchangelog-file and combine them on release?

the first solution has the drawback of constant mergeconflicts...

has anyone opinions or other suggestions for this topic?