Add method for adjusting gif loop setting

[andrewheiss]

When writing an animated gif, the convert command allows you to set a flag for how many times the gif should restart (with 0 = ∞):

convert -loop 0 -delay 100 ... animation.gif

It's possible to set frame delays with Wand

for frame in img.sequence:
    with frame:
        frame.delay = 100

But there's no way to mess with the loop setting:

img.loop = 0  # Doesn't work, obviously

Is there some other way to set arbitrary ImageMagick options, or does this just not work?

[dahlia]

It seems possible to implement using MagickSetImageProperty() C API e.g. MagickSetImageProperty(wand, "loop", "0").