Accept RDF datatypes in RDF/XML parser (#223)

* fix: accept XMLLiterals

* fix: also support unexpected data types

* fix: corrected after review by althonos

pronto/parsers/rdfxml.py

@@ -173,7 +173,7 @@ def _compact_id(self, iri: str) -> str:
             match = re.match(f"^http://purl.obolibrary.org/obo/{id_}#(.*)$", iri)
             if match is not None:
                 return match.group(1)
-        return iri
+        return iri 
 
     def _compact_datatype(self, iri: str) -> str:
         match = re.match("^http://www.w3.org/2001/XMLSchema#(.*)$", iri)
@@ -182,6 +182,9 @@ def _compact_datatype(self, iri: str) -> str:
         match = re.match("^http://www.w3.org/2000/01/rdf-schema#(.*)$", iri)
         if match is not None:
             return f"rdfs:{match.group(1)}"
+        match = re.match("^http://www.w3.org/1999/02/22-rdf-syntax-ns#(.*)", iri)
+        if match is not None:
+            return f"rdf:{match.group(1)}"
         raise iri
 
     def _extract_term_relationship(