[sdiy] analogue phase modulation

[JH.]

>One point back then was that the "modulo" function required would lead
>to discontinuities in the form of glitches, where artefacts could occur.

I had _expected_ the need for an elaborate wavefolder.
But when a range of +/-Pi is enough, the waveshapers would be very simple.
One full wave rectifier to create a "triangle cos", and two full wave 
rectifiers to
create a "triangle sin". Then two triangle to sine converters.

JH.