Fixed problem serializing Rudolf objects

Explained the to-string convenience function

Merge branch 'main' of github.com:quoll/donatello

Fixed and debug printing removed

Merge branch 'main' of github.com:quoll/donatello

Added a test for long path URLs with a prefix that matches the context

Fixed IRI syntax error for XSD time types

Merge branch 'main' of github.com:quoll/donatello

Bumping version

Addressed duplicate prefix keys with different key types