Basics for handling RDFPost

Still need to connect www-form-urlencoded to the rdfpost hander
Also, first draft of affordance.
Documentation changes
Updated to RDF 1.1
Refactoring RDFa writer

Want to be be able to build Affordance based HTML responses
Added RDFaWriter

Based on RDF::RDFa::Writer - reworking into smaller classes before
adding affordance recognition and RDFPost setup
Completed big refactor of RDFa writing

Loosely based on the original rdf-rdfa RDFa::Writer class, decomposed
into smaller pieces. In prep for supporting affordance describing graphs