1.12.3 Add ch32 support

What's Changed

• Add ch32 support by @hathach in #397

This release adds support for ch32 core with bit banging implementation.

Tested with ch32v203g6 qtpy with neopixel featherwing (32 pixel) work with multiple F_CPU: 144mhz, 120mhz, 96mhz, 72mhz, 56mhz

Full Changelog: 1.12.2...1.12.3