Let right/left arrows scroll horizontally in slmenu

[stianhoiland]

Been using Yori more and more lately, and found myself using slmenu to give me a selectable summary of say a file search. But especially with file searches the path takes up too much horizontal space to be useful; I can't see the filename. And right/left arrows don't scroll the menu horizontally, so it becomes useless.

Maybe this horizontal scrolling could be something to implement (oh, and if you do, don't make it scroll character-by-character. Do a third or a half of a width.)?

[malxau]

I added automatic horizontal scrollbars and left/right arrow support in commit c19cd12 .