Function: add_bleed_edge

--Usage--
> add_bleed_edge(input: image, horizontal_size: number, vertical_size: number, background_color: color)

Add a crude print bleed edge around an image.
The sizes are given in percentages of the image size, so @horizontal_size: 1@ makes the image three times as large by putting a bleed edge of 100% on both sides.

--Parameters--
! Parameter				Type				Description
| @input@				[[type:image]]		Image that needs a print bleed edge
| @horizontal_size@		[[type:double]]		Size of the bleed edge on the sides, in percentage of the image width. Optional, defaults to 0.048
| @vertical_size@		[[type:double]]		Size of the bleed edge on the top and bottom, in percentage of the image height. Optional, defaults to 0.037
| @background_color@	[[type:color]]		Background color, optional, defaults to transparent