implement a minimal git dirty logging
Minimal version that assumes a git executable to be available.
Git hash and diffs of any dirty files are now logged into a file dirty in an output folder.
A cleaner solution would use the LibGit2 stdlib. However, that does not (yet) expose commands to query dirty files and commit hash of selected git commits (I think).
At least I remember that I tinkered around with C bindings a while ago, but now I can't those anymore ...