made methods public. refs #134
extracted serialiseLiteral() into separate method. refs #134
use escaped uri (typo?)
get string representation of resource-uri explicitly
extracted IRI-encoding into separate method. refs #134
reuse id-encoding method. refs #134
Merge pull request #134 from indeyets/turtle-serialisation-public

Made internal functions in the Turtle serialiser public, so that other classes can use them.