Okay, here goes another patch:
* Topaz metadata support (shamelessly ripped out of Calibre from GRiker's code, so thanks!)
* Kindlet metadata support, since it was bugging me, and it's pretty simple (Should handle both official & developper apps. A developper app (ie. no ASIN) will print a warning message to the console, but that's harmless, the Kindle software falls back to the usual SHA1 hash too in that case).
At first glance, it seems to work, both read and write, but I haven't tried a tweaked collection db on a live device yet.
Again, forgive my brute force approach to Python

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EDIT: Attachment removed, patch merged upstream.