update methods in ASSLineContents for comments support; fix typos
ASSTags: fix copy method; comment broken remove method; fix typo in ASSLineContents:insertSections; force reference updating for callback methods when an object was replaced; fix tag deduplication for new ASSLineTagSection class; fix typo in ASSLineContents:splitAtTags(); add methods for getting tables of currently effective tags in LineSections; chose better names for some methods