Implement the --lines option

[fabianscode]

tested with various options and scale

[sid115]

If the number of lines is greater than the number of items, empty lines are added at the bottom of the menu. In my opinion, empty lines should be cut off like in the implementation of --lines in dmenu.

Also, in my opinion, it feels more natural to scroll through items in a vertical layout using the up and down arrow keys instead of left and right.

Other than that, everything works as expected.

Tested on NixOS 23.05 with an overlay using an edited dmenu-wayland's nix file to use this fork instead.

I am not familiar enough with C to contribute to this project, but I am happy to test changes and provide feedback if desired.

[fabianscode]

Thanks for reviewing!
I agree with you on the arrow keys.
But since the original dmenu also does not implement dynamic height depending on the amount of non-empty lines, I suppose it would be better to simply make this functionality available through a patch.

[fabianscode]

@nyyManni could you take a look at it, please? :)

[fabianscode]

@sid115 arrow keys should be implemented now