Fix a readme type
Add support in geoserver-ext for axis filters

This commit will add support for axis filters for additional
"non-standard" axes instead of only the standard axes. Needed this for
the POI demo.
Improve PA Axis classes to support more functions

This commit will improve the NominalAxis and MetricAxis to support more
functionality, e.g. MetricAxis now has a working splitAxis function in
its IntegerIndexer. Additionally NominalAxis can now be used without
having to initialize it with a WordList.
Add a new demo based on POI's OSM data

This commit will add a new demo that is based on POI's extracted from
the Netherlands OpenStreetMap dataset.