Version 2.1.
Use updated rdf-reasoner with OGP literal datatype support.
This addresses issue #19.
Allow language-tagged string to match schema:URL.
Update dependency on rdf-reasoner to 0.2.1.
Fix test for language-taged URL.
Release 2.1.

* Use updated rdf-reasoner with OGP literal datatype support. This addresses issue #19.