This is a little hacky but at least very simple implementation of a feature requested in #59. With this change, one can get rid of the tip of the arrow by pressing ctrl key, getting straight line instead.
If you're OK with this idea, I can add appropriate documentation and whatever else is needed. If you think we should instead have a separate button for line mode, I can add make such PR instead of this one.
This is a little hacky but at least very simple implementation of a feature requested in #59. With this change, one can get rid of the tip of the arrow by pressing ctrl key, getting straight line instead.