RGDA1 for RDFlib

RGDA1 (RDF Graph Digest Algorithm 1) combines the traces graph labeling algorithm with the Sayers and Karp RDF graph digest algorithm. This algorithm will produce canonical cryptographically unique identifiers for any RDF graph.
are the runtime and call_count decorators needed for anything but the benchmark example?
Should they be private? (Usually classes are meant to be CamelCased according to [PEP8](https://www.python.org/dev/peps/pep-0008/#class-names))