Update with nulled printf (to prevent warnings on non-printf projects) and undestructively add interrupt nesting to WS2812B driver.

Fix for UART fractional BRR caclulation

 * Allow interrupt preemption in WS2812B driver.
 * Add simple driver for ws2812b's.

tim2_encoder example based on tim2_pwm_remap

Add #ifdef support for CH3/CH4 in tim2_pwm example

Avoid bricking CH32V003J4M6 - For #219

-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

Blink LED pin D6 as well (for MuseLabs nanoCH32V003 boards)

These boards have an LED on D6

https://github.com/wuxx/nanoCH32V003

Let me know if this causes anyone issues.

Remove redundant debug shell scripts

Issue #212 fixes - examples fail to compile

Update minichlink to not reset when writing bootloader.

Disable DEBUGPRINTF I/O when FUNCONF_USE_DEBUGPRINTF = 0

Isochronous adc example

Clean up #define situation for SYSTEM_CORE_CLOCK, APB_CLOCK, USE_HSI/HSE

sysclk fixes and example project

SYSTEM_CORE_CLOCK went away in favor of FUNCONF_SYSTEM_CORE_CLOCK

APB_CLOCK is only used in the i2c_slave.h and ch32v003_SPI.h files
so the references there have been maintained.