dfitoimd: decoding Intel M2FM floppy flux images (was Re: Intel 432 floppy flux images for decoding)

Because the cwtool support for Intel M2FM floppy disk flux images isn't publicly available, I've written a crude Python 3 program for converting such images (in DFI format) to ImageDisk images, and put it on github: https://github.com/brouhaha/dfitoimd My ADPLL data separator has parameters to control the proportions of frequency adjustment and instantaneous phase adjustment that are done at each flux transition. I've experimented with the parameters quite a bit, but it's still not good enough to reliably recover all sectors are currently 0.5% frequency adjustment and 10% instantaneous phase adjustment. I was actually fairly surprised that I didn't get better results with more frequency adjustment and less instantaneous phase adjustment. It's entirely possible that my algorithm isn't very good. The code can handle normal IBM 3740 single-density FM format as well, though there are other published programs that already do that. There's a start at code for IBM System/34 double-density MFM format also, but it hasn't been tested at all as I don't happen to have any suitable DFI images. The dfitoimd program is quite slow; on a typical Intel M2FM image with two revolutions per track and 25 MHz sampling, it takes 64 seconds on a 4.0 GHz AMD CPU. I'm pretty sure that rewriting it in C/C++/C# or the like would make it much faster, but I specifically chose Python as I find it easier to experiment with the algorithms.