Add `[O`, `]O` and `cO` map groups to change all windows

[blueyed]

I found this quite handy for a while already.

If it gets accepted, documentation should be added, of course.

[blueyed]

I've amended the initial commit (ca1411c), and rebased it on master.

[blueyed]

@tpope Do you like the idea? It allows for cOn to toggle line numbers in all windows at once.

[tpope]

It's not a bad idea. Outside of 'number' I am not sure it will get much use. And I really hate going down the windo rabbit hole. (You're a first hand witness to all the trouble it has given me on fugitive.vim.)

How hard would it be to make the toggle variant put all windows into the same state? Having it toggle on some and off some seems pretty useless.

[blueyed]

I really hate going down the windo rabbit hole

Yeah, that's unfortunate, but manageable.

How hard would it be to make the toggle variant put all windows into the same state? Having it toggle on some and off some seems pretty useless.

It uses the same state for all windows, based on the current window. Probably because the C-R>=<SID>toggle() is evaluated before the windo.

[tpope]

What's your stance on the usefulness for other options? cOn is a bit awkward to type, so I'm wondering if we fudge things a bit and just always windo for 'number' and possibly 'relativenumber'.

[tpope]

We're probably going to need special casing anyways, as :set number in :help is almost never what you want.