These boards have an LED on D6

https://github.com/wuxx/nanoCH32V003

 * No more needing to decide between printf and UART in code.
 * Better debugprintf input
 * Unified code for all clock sources.
 * TINYVECTOR now saves like another 120 bytes of space.
 * None of the `Makefile`s except `bootloader` need anything extra
 * All configuration via `funconfig.h`
 * Sane defaults.
 * `SystemInit()` also initializes debugging (UART or SWIO depending on configuration)
 * Tunable timeout on debug printf.
 * Configurable UART baud rate.
 * `funconfig.h` is automatically included by `ch32v003fun.h`
 * Paves the way for other, non-003 processors.

Cleanup some comments.

Add ability to use vendor commands with programmers.

* Blink now blinks D4 too
* Don't use compressed instructions by default.  Some compilers are old.
* Prevent double-halting on linke programmer.

Update build instructions on Windows to show how to use the off-the-internet build chains instead of WSL2.

Also fix 2 warnings.

Switch over to using a .c file instead of a .S file for the startup code.  Helps make order-of-compiling not matter.

It crashes because of idiv.