Added IE < 9 support with excanvas

Great plugin, thanks for creating it!  I had a use-case recently that required support for IE < 9 using excanvas.  This pull request adds support for excanvas + IE7/8.    

IE 8 required adding the canvas element to a container that had no "P" tags (I used body but only if excanvas is loaded).  Also IE 8 standards requires calling initElement again after any non-canvas changes are made (such as height/width) while IE7 must call it before any changes--yeah very ghetto.

I had to change jQuery code in prepareCanvas function to plain JS to make excanvas happy as well.

Maybe it will help someone else stuck writing for archaic organizations.  Thanks again.

Tested on Chrome (Mac), IE 7/8/9 (Windows 7).