Version 1.1.4.
Finish 1.1.4.

* Update Reader.open documentation to indicate that using the return value as a reader is not well supported, and implementations should restrict themselves to working within a block
* Implement Node#intern using cache, so that Node(\"b\").eql(Node(\"b\")).
  This also allows Statement(:s, p, :o) to eql? Statement(:s, p, :o), where previously the nodes would not be the same.
* Added missing Enumerable#enum_for; it was previously just in Countable and Queryable.
* Major changes to Vocabulary:
  * Refactor Vocabulary using class instance variables.
  * Change RDF vocabulary to delegate to RDF::RDFV, allowing definitions for RDF properties, classes, datatypes along with comments and labels.
  * Implement Vocabulary::Term as subclass of URI used for vocabulary terms. This now implements Vocabulary::Term#label and Vocbulary::Term#comment in addition to Vocabulary.label_for and Vocabulary.comment_for.
  * Implement Vocabulary.to_graph to generate RDF statements for a ruby Vocabulary definition.
  * Change Vocabulary#to_graph to Vocabulary#to_enum (and #enum_for), basically doing the same thing, but avoiding emergent problems.
  * Rename HTTP vocabulary to HT, to avoid unfortunate prefix, and to be consistent with general use.
  * Describe fuller vocabulary DSL.
  * Implement Vocabulary.expand_pname.
  * Update vocabulary generation to serialize all properties (with no language or language \"en\")
  * Update all built-in vocabularies.
  * Use our own version of xsd RDFS vocabulary. Update RDF vocabulary.
  * Implement respond_to? and method_missing for Vocabulary::Term to create attribute accessors.
  * Move vocabulary loading from CLI method to Vocabulary.load; use for generating vocabularies.
  * Add RDF::Vocabuarly.find and .find_term to lookup URIs.
  * Remove Data-Vocabulary vocab (RDF::V).
  * Initialize vocabulary terms with the vocabulary it comes from; add Vocabulary::Term#vocab to retrieve this.
* Implement URI#pname to create a string form of URI#qname.
* Add :unique_bnodes option to writer to ensure that BNodes are uniquely serialized, in spite of any identifier used when they are initialized.