nrf: implement rotaryio.IncrementalEncoder

[dhalbert]

There is a QDEC (quadrature decoder) peripheral that does the work.

[dhalbert]

Discussed this: better to use a timer so we can have more than one instance.

[Tasm-Devil]

Can't wait to try this rotaryio on my nrf52840 Express.

[ladyada]

@Tasm-Devil you can help @nickzoic beta test :)

[nickzoic]

That's be great!  I've got the hardware on the bench, I'll have a PR in the next few days ...

[Tasm-Devil]

@ladyada I'm glad to do so. I have it on the table too.