This is needed so that the floppy flux reader can enable the pull up
on the index pin while using it as a pio jmp pin.
Also fixes a doc bug where the `jmp_pin` was omitted in one spot in the docs.
At present, Adafruit's rotary encoders all move 1 quadrature cycle per
detent, so we originally hard-coded division-by-4. However, other
encoders exist, including ones without detents, ones with 2 detents per
cycle, and others with 4 detents per cycle.
The new `divisor` property and constructor argument allows selecting
a divisor of 1, 2, or 4; with the default of 4 giving backward
compatibility.
The property is not supported (yet?) on espressif MCUs; it throws an
error if a value other than 4 is set.
Any two consecutive pins can be used for an IncrementalEncoder
Testing performed: Put a synthesized (few hundred counts per second) quadrature signal into GP2/3 and read the encoder out. Performed filesystem operations at the same time to stress test it.
The reasons for not using common_hal_rp2pio_statemachine_readinto are commented on.
