with the hook in Parser::clearState() makes sure the state of the Object is
kept in sync with the state of the parser, i.e. works correctly for dumpHTML
* give <ref> and <references> a css class, reference and references, respectively
* Code cleanup
* Lots of documentation, every function fully documented + code comments
* Split link() into linkRef() and linkReferences()
* Split key() into refKey() and referencesKey()