Use singleton list if only single annotation is used.
Use singleton sets for first value; switch if second value is added.
fix #297 ManchesterSyntax rendering prints annotations twice.
Merge pull request #296 from sesuncedu/version4_singletons

Singletons for annotations and MapPointer value sets (first cut)
Do not ignore any round trip tests.
Do not stub out failing round trip cases either.
 Don't force addMissingTypes to false for RDF Formats, whilst leaving it set for others.
 (With JSONLD ignored), this reduces the number of failed tests from 26 to 14.

 With missing types added, there are 5 test cases with failures.
 Without missing types added, there are 8 test cases with failures.
Test negative data property value assertions that are xsd:string and PlainLiterals (currently fails for JSON-LD.
Ignore JSON-LD until decision on whether/how to make it round trippable.
(The JSON-LD parser/renderer are aggressive about removing and adding xsd:string from plain literals with no lang
 tag)
Don't print failure message to stdout.
Don't include stack trace in message string (leave it to the JUnit)
Allow RDF Document formats to be both Prefix and non-Prefix aware.

Prefix Ontology Format Test Case now passes.
Extraneous restriction to Rio Prefix formats in method not under test.
Address some of the roundtrip issues in #299

Tests still not all passing - the test change knocked off a manchester
syntax test, and the DataUnionOf test is still broken
Fix man syntax test failure. Still failing on DataUnionOf
Hasher, equality tester, and Trove custom hash strategery for comparing OWL Objects matching xsd:string to PlainLiteral with no language, and rdf:langString to PlainLiteral with lang tag.

New code used in round trip test.

JsonLD brought under test.

JSONLD marked as non-Prefix aware.
Remove overrides hiding possibly failing tests  - if a test  isn't passing, it should be seen to fail, or should be explicitly ignored.

 Ignorance isn't bliss.

 [oddly, some of the tests actually pass, and a few  RDF/XML renderings throw errors]
Use correctly formatted urns (maybe we ought to check for this).
Use correctly formatted urns (maybe we ought to check for this).
When pushing triples from RIO Turtle parser to RDf consumer, 
blank nodes should have _: not #

Bit of a hack, really.
JSONLD makes plain literals into xsd:string literals

Adapted test to take this into account