[AD] Display option change function

[Trent Gamblin <trent@xxxxxxxxxx>]

I think we need such a thing now, I'll explain why.

For platforms with rotatable screens (currently ios) we have a display option that controls which orientations are supported. There are a number of good reasons you would want to change this (in my case I want three options: one that auto rotates between both landscape modes, and one each to fix rotation on each lanscape mode.) Problem is display options get set on display creation and so setting them again only has effect on new displays.

First I thought I would add a separate function, al_set_supported_display_orientations, but there are problems, namely where to store this information. It has to be stored in a display, but has to be settable before the display is created. I could make the function cache the values and all that, but it seems to me the best solution is just having an al_change_display_option function and that's what I'm proposing. We can document which options can and cannot be changed.

Any reason not to add this?

Trent