ASSTags: remove costly table.insert calls from ASSLineContents:new()
ASSTags: remove costly table.insert function calls from ASSLineContents:get()
ASSTags: add support for unknown tags
ASSTags: support comments mixed in with tags. They always get dumped at the end of the section, see if I care. If you're mixing comments with tags, you are beyond help, anyway. Also remove costly table.insert function calls from ASSLineTagSection