v3

These updates for version 3:

* Simplify functional model - tags can now be inserted with anywhere `Ctrl/Cmd` shortcut -- containing tag is no longer considered. Containing tag can be changed with `Ctrl/Cmd-Shift` shortcut. 
* Edits now backed out with single undo
* Multi-cursor support
* Help panel is now created using custom user data
* Added unit tests
* Fixed split/join