Merge pull request #260 from mmd-osm/patch_area_delta

> Maybe we could also have a unified rules file instead and remove <changed since="{{area_version}}" until="{{area_version}}"/> in case of a normal run?

We can get a unified rule set of the "changed" statement as follows:
- the changed statement accepts a special value "init" for since
- for this value its semantics is to accept anything
Then we only need to sed for "init" instead of area_version in the script.

I'll make a commit on top of this pull request.