I've made some significant improvements in several aspects:

1. Scrolling: performance and behavior
2. Selection entire lines by dragging over line numbers
3.  Color config: a separate highlighting setting for line numbers, which takes effect immediately

I've also remove the Tk version >= 8.5 check, and replaced the hack for getting font updates to take immediate effect.


As far as I can see, the only things left to resolve are:

1. Clear, consistent behavior regarding whether line numbers are enabled by default, and when and how this default is changed.
2. Menu item location, type (boolean flag?) and correctly reflecting the state of each window.