All vocabs moved from `RDF` module to `RDF::Vocab` (closes #21)

Version 0.3.0

/cc @jpstroop @acoburn @no-reply @jcoyne @mjgiarlo @gkellogg Note that, for some reason, in re-generating the vocabs into the new modules (technically, I could have simply edited the files to change the module names) the vocab-loader appeared to detect other vocabs and replace base URIs with prefixes.  I don't know that that's a problem, but I'd like someone with more experience in this area to weigh in.  Probably a really good idea to have some vocab-specific tests, too?  In any case, I see now how we might need to create V1 vocabs for MODS and MADS ...  I don't think this is new behavior for RDF.rb, since I can see that other URi-prefix replacement happens (e.g., skos, owl) presumably from knowledge of those vocabs automatically loaded by RDF.rb.