Update Turtle parser to current W3C Working draft

The Rio turtle parser and writer are currently based on the 2006 version of the Turtle format as defined by Dave Beckett (see http://www.dajobe.org/2004/01/turtle/ ). However, W3C is officially standardizing Turtle, currently it's a working draft (see http://www.w3.org/TR/turtle/ ). Our Turtle parser should be updated to reflect this updated spec. A partial was already done to address one specific incompatibility (see ), but we need to review the spec and the parser/writer in more detail to flush out any incompatibilities.