closes #3

- this transforms
  - rr:graph statements to equivalent rr:graphMap [ rr:constant ... ]
    statements
  - rr:subject statements to equivalent rr:subjectMap [ rr:constant ... ]
    statements
  - rr:predicate statements to equivalent rr:predicateMap [ rr:constant ... ]
    statements
  - rr:object statements to equivalent rr:objectMap [ rr:constant ... ]
    statements
  - rr:class statements to separate rr:predicateObjectMaps with rdf:type
    as predicate map constant and the assigned class as object map
    constant