readline(1) improve readline editing (enabled by default)


A support package that tries to make editing with readline easier. At the moment, it reacts to clicking shift-left mouse button by trying to move the text cursor to this position. It does so by generating as many cursor-left or cursor-right keypresses as required (this only works for programs that correctly support wide characters).

To avoid too many false positives, this is only done when:

- the tty is in ICANON state.
- the text cursor is visible.
- the primary screen is currently being displayed.
- the mouse is on the same (multi-row-) line as the text cursor.

The normal selection mechanism isn't disabled, so quick successive clicks might interfere with selection creation in harmless ways.