Extensive rework of ID15 (Direct) handlers. 44kHz reproduction now supporting and working, tested, on Arduino Nano, Thinary Every @16MHz , Seeed Xiao M0 (SAMD21)

[stripwax]

This was a fun project :-)

[stripwax]

Oh, I should add what I've tested. Not everything worked, but it didn't work before either.. my Seeed Xiao is my reference standard at this point. Regular tap loaders, turbo, polarity-sensitive, and a number of ID15 loaders, including 44kHz OTLA loaders. Most of them work, but I couldn't yet find a working OTLA example. Digital output looks good, so I suspect something in the analog stage is messing things up (and this is going through a cassette adapter into Spectrum +2, which is not a high-fidelity solution).

However, I have not tested anything for non-Spectrum machines; and my changes have a small number of CAS playback changes which ought to be tested

[rcmolina]

Chapeau!