more tests with umlauts
more diagnostics in check_geocoding
more work on Strassen::Lookup and GeocoderAddr

Major changes: try to make case insensitive searching possible. To be
correct, this is using Unicode::Collate. More test cases were added.

The current solution feels still somewhat hackish, but with recent
versions of Unicode::Collate and Search::Dict, at least the test suite
passes.