Function: set_combine

--Usage--
> set_combine(input: image, combine: combine_mode)

Set how the resulting image should be combined with the background.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:image]]		Image to change combining mode of
| @combine@	[[type:combine]]	Combining function to use

--Examples--
> set_combine(input: "image1.png", combine: "shadow")  ==  [[Image]]

--See also--
| [[fun:combine_blend]]		Blend two images together using a given [[type:combine|combining mode]].