Sprite generator for Elgg

Instructions
=================
 1. Place sprite icons in a directory. They should be named like this:
<icon name>_icon&16.png for normal icons and <icon name>_hover_icon&16.png
for hover icons. The "_icon&16.png" section is ignored except that icons
must end in ".png".

 2. Run the sprite generation code: php sprite.php -d ~/<my directory/
This produces the sprite png file and a css file.

 3. Copy the sprite file over Elgg's sprite image and copy the text from the
the css file and paste it into the icon css elements view.


Gotchas
================
The code does not handle icons of different widths. Also, if there are icons
that are being used for two selectors, these exceptions have to be hard coded
into the script.