Function: enlarge_image

--Usage--
> enlarge_image(input: image, border_size: amount_to_enlarge)

Enlarge an image by putting a transparent border around it.
The border size is given in percentages of the image size, so @border_size: 1@ makes the image three times as large by putting a border of 100% the size on all sides.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:image]]		Image to enlarge
| @border_size@	[[type:double]]		Amount of border to add, in percentage of the image

--Examples--
> enlarge_image(input: "image1.png", border_size: 0.1)  ==  [[Image]]
>>> enlarge_image(input: <img src="image1.png" alt='"image1.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />, border_size: 0.1) == <img src="image_enlarge.png" alt='"image_enlarge.png"' style="border:1px solid black;vertical-align:middle;margin:1px;" />