Feature request: Support arithmetic coding

It would be nice if your script could support arithmetic coded JPEGs.  Example: http://filmicgames.com/Images/Patents/bedroom_arithmetic.jpg

Chromium supports them natively, but Firefox does not.  https://bugzilla.mozilla.org/show_bug.cgi?id=680385

It would be nice if your script did support them, so that browser support didn't matter.
