* Renamed some symbols for consistency, fixes#6:
- yamlStartSequence -> yamlStartSeq
- yamlEndSequence -> yamlEndSeq
- yamlStartDocument -> yamlStartDoc
- yamlEndDocument -> yamlEndDoc
- yTagMap -> yTagMapping
* Improved code formatting at some places
* Fixed code documentation at some places
* Added generic objects to TODO list
* Removed obsolete parsing tests, these are superseeded
by yaml-dev-kit test suite integration
* Added PresentationOptions object; merged PresentationStyle,
indentationStep and NewLineStyle in it
* Updated signatures of relevant procs
* Implemented user-defined newline style in presenter
* Added serialization.txt to doc
* Fixed rendering problem in api.txt
* Use explicit tag when ref type renders to a scalar that can be
parsed to !!null
* Added test cases for this ref type fix