Has 2 failing specs...
There are still some issue with this code's interaction with the undo
system. The tab stops will need to be or destroyed when certain
changes are undone or redone.
For this to work, I needed to make the updating of anchors transactional. Now, all anchors are updated and *then* they emit their events. That way when the cursor moves based on the user typing, the tab stop they're in has a chance to expand before we handle the move event. This prevents spurious cancellation of the snippet when typing on a tab stop.
Add the 'strong' option to anchors. If anchors are 'strong' instead of being destroyed by encompassing changes they move to the beginning of the change range.
Cursors and selections no longer need to handle buffer/display-buffer changes directly. They register anchors with the EditSession, and subscribe to changes in their position instead. This opens up the anchor facility for use by extensions that want to track the screen position of a point in the buffer as the buffer and display buffer change.
This allows Cursor.proto.moveRight to avoid pre-clipping its position. It just passes the appropriate clipping options when setting its screen position.
