This pull request provides a first implementation of the GeoSPARQL query rewrite extension (section 11 of the document).

All 4 scenarios are handled i.e.:
Feature-Feature
Feature-Geometry
Geometry-Feature
Geometry-Geometry

The implementation does not perform a check on whether a class is a subclass geo:Feature in the ontology, but applies a strict check on the object property geo:hasDefaultGeometry. The latter assumption can be relaxed or expanded in the code.
Beyond the core requirements of the GeoSPARQL standard, no additional features are implemented at this time. However, all topological functions are covered.

Via this implementation the query:

?geo1 geo:hasDefaultGeometry ?geom1 .
?geom1 geo:asWKT ?xWkt .
?geo2 geo:hasDefaultGeometry ?geom2 .
?geom2 geo:asWKT ?yWkt .
FILTER(geof:sfIntersects(?xWkt, ?yWkt)) .

can be shortened to

?geo1 geo:sfIntersects ?geo2