add insert_image and add_bleed_edge functions

doc/function/add_bleed_edge.txt

@@ -0,0 +1,15 @@
+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
+

doc/function/enlarge.txt

@@ -9,7 +9,7 @@ The border size is given in percentages of the image size, so @border_size: 1@ m
 --Parameters--
 ! Parameter	Type			Description
 | @input@	[[type:image]]		Image to enlarge
-| @border_size@	[[type:double]]		Amount of border to add
+| @border_size@	[[type:double]]		Amount of border to add, in percentage of the image
 
 --Examples--
 > enlarge(input: "image1.png", border_size: 0.1)  ==  [[Image]]

doc/function/index.txt

@@ -89,6 +89,7 @@ These functions are built into the program, other [[type:function]]s can be defi
 | [[fun:recolor_image]]		Change the colors of an image to match the font color.
 | [[fun:resize_image]]		Stretch or squeeze an image to a given height and width.
 | [[fun:enlarge]]		Enlarge an image by putting a border around it.
+| [[fun:add_bleed_edge]]		Add a crude print bleed edge around an image.
 | [[fun:crop]]			Crop an image, giving only a small subset of it.
 | [[fun:flip_horizontal]]	Flip an image horizontally.
 | [[fun:flip_vertical]]		Flip an image vertically.