Add DDI-RDF Discovery Vocabulary

[grosscol]

Description at http://rdf-vocabulary.ddialliance.org/discovery.html
Turtle specification is: https://raw.github.com/linked-statistics/disco-spec/master/discovery.ttl

[grosscol]

Went to work on this, but ran into issues when trying to run rake tasks. bundle exec rake -T will yield an error:

LoadError: cannot load such file -- rdf/cli/vocab-loader
/home/grosscol/workspace/rdf-vocab/Rakefile:7:in `require'

Chalking this up to in flux state of the 2.0 beta. I'll check back and try generating a vocab again later.

[gkellogg]

That's because edge.rb Devon has changes not synced to rdf-vocabulary quite yet. If you fork the 1.99 mains nance branch, and make sure Gemfile does not use github refs, it should work okay. Otherwise, I'll get to it shortly.

[gkellogg]

Note that the discovery vocabulary has a minor error: linked-statistics/disco-spec#220. I'll address that in a patch file.

[gkellogg]

Also disco:Representation class is undefined.