2.0.0.beta2

respond_to_missing in RDF::Query::Solution
Freeze Literal, Node and URI values on instantiation.
Freeze Term#to_base result.
Use symbol, rather than string, to index intern cache.
Change "rdf" executable to take a pipeline of commands, so that multiple commands can be stacked.
Remove vocab-fetch
Deprecate Vocabulary.load in favor of Vocabulary.from_graph.
Change vocabulary generation in Rakefile to use rdf cli.