Display window line numbers

[Juri Linkov]

I wonder why ‘display-line-numbers’ doesn't provide an option
to display line numbers relative to the window-start?
IMHO, one of the most reasonable excuses to sacrifice the screen space
for line numbers is to display only these short numbers that could be
used to jump to a line visible on the screen.  For that the quickest
key sequence is e.g. 'M-5 M-r'.

Then all possibilities will be covered by these options of
‘display-line-numbers’:

- absolute line numbers can be used by 'M-g M-g' (goto-line);
- relative line numbers - by 'C-u N C-n' and 'C-u N C-p';
- window line numbers - by 'M-r'.