[jQuery] MarkItUp image upload

I've just created an improved image widget for the MarkItUp editor[1].
Instead of being prompted for an existing URL for the src attribute, a
file upload form is created. The form target a hidden iframe. An
online script should return the URL, as well as the final width &
height. When the iframe has loaded, the dta is used to create the img
tag. Voila!

You can see the code here:

http://pastebin.ca/1763467

This example requires both jquery.loading & jquery.json (and a
'cancel' button image). I fully expect that others might want to do
things a little differently.

b

[1] http://markitup.jaysalvat.com/home/