bump to sbt 0.13.2
fixes the serialization of relative graphs in Jena
IMPORTANT CHANGE: the RDF model is as of RDF 1.1! Rdf#Literal is now
concrete
Update .travis.yml
moved the implicits for TypedLiteral and LangLiteral into Literal
adapted the test suite to the new model
reflected the new RDF model into banana-jena
reflected the new RDF model into banana-sesame.

This is relying on upcoming Sesame 2.8 series because of its very decent support for RDF1.1.
Return Some[X] for extractor when it cannot fail
prefix datatypes in JenaOps with __ just as a convention for saying this
is local (don't want to use modifiers)
Merge pull request #101 from w3c/rdf11

Make banana-rdf RDF1.1 happy
First pass as Plantain, an immutable RDF implementation in Scala.

URIs are from Spray and the Turtle parser/writer are from Sesame.
refactoring in PlantainTurtleWriter
implemented graph diff in Plantain
Implemented Graph isomorphism for Plantain using Sesame's
small refactoring in TurtleTestSuite to rely on typeclasses
wired test for Turtle parser/writer in Plantain
wired all tests that could be wired in Plantain
All methods in URISyntax are directly derived from URIOps.

URIOps is now required for RDFOps and a DefaultURIOps is made available.
Provided a custom PlantainURIOps.

PlantainURIOps.relativize() still relies on java.net.URI because
spray.http.Uri does not expose a similar method.