This is something I've been waiting a while for!
Alchemy is a technology which makes it possible to convert code libraries from other languages, such as C, into ABC (Actionscript Byte Code) which is the underlying technology behind the Flash Player. In other words, you can take code libraries from other places and use them in the Flash Player, without any additional dependencies. It's not easy mind you, but it is very cool.
I still haven't figured it out myself, so I've been impatiently waiting for someone else to be nice and figure it out for me. Which they just have!
What actually interests me the most about this is the fact that it adds .raw image support to the Flash Player, which is very much something that I'm interested in getting into ImageSizer. Expect the next major release to include .raw image support!