Replace separate implementations of #empty? in Graph and Repository with the Countable version, which should be optimal. This addesses issue #115.
Update Graph spec to check for Repository behavior.
Update List specs.
Fix bug noted in issue #114, where Query.execute defaults patterns to nil, when it should be {}.
Created Query::Solutions spec based on examples.
Massive update to create RSpecs for most documentation examples.
Include rdf-rdfxml gem when testing.
Mark pending on odd rubinius problem with solutions offset.