Made partitioning function of groupify generic.
Improved error reporting of groupify.
Characteristics of properties are now specified by keywords
rather than vars resolving to functions.
Default ontology was being mistakenly used in guess functions.
dataproperties also use keywords now.
Inclusive and exclusive were the wrong way around.
Reworked literal support.
Tests for groupify-at
Default ontology checks restored.
New Tests for datatypes.
Documentation update. Pointless call to toURL removed.