Added tests for getOrSaveUnique
Implemented getOrSaveUnique
Added saveUniqueOrFail tests
Added saveUniqueOrFail functions. Closes #110
Tests for saveUnique alias
Implemented aliased uniqueness functions
Renamed rel.saveUnique to rel.createUnique
Added uniqueness documentation
Fix typo in saveUnique docs
Fixed typo in node.saveUnique
Add re-reads to uniqueness tests
Merge pull request #112 from jonpacker/unique

Add API for uniqueness functionality