my head hurts. I can squash commits if this is getting out of hand

fixed path to ch32v003fun

Improve I2C slave library, handle stop condition properly, add secondary address listening, remove GPIO configuration

count variable does not do anything

Signed-off-by: Amitesh Singh <singh.amitesh@gmail.com>

Make top comment section match project.

-Implement CH3 and CH4 optionally via #define
-By default only CH1 and CH2 are enabled.
-Channels 3 and 4 can be enabled by uncommenting the appropriate line
-Choose whether default of PWM pins is HIGH (0xff) or LOW (0x00)

NOTES:
-Channel 3 is on a different port (GPIOC) which will be enabled if
needed.

-Channel 4 is on the NRST pin so not usable unless you use `minichlink -d`
to disable the NRST function so the pin can be used as a GPIO

-If your board has a bypass capacitor on PD7 for a reset button the
waveforms observed on CH4 will not be nice square waves.

Uses partially remapped pins to read a rotary encoder (or any quadrature
input) using pins that should be 5V tolerant

These boards have an LED on D6

https://github.com/wuxx/nanoCH32V003