WS2812 driver

Upload with serial to the bluepill:

1. Set boot0 to 1
2. Leave boot1 to 0
3. stm32flash -w main.bin -v /dev/ttyACM0

Upload with ST-LINK:

1. st-flash write main.bin 0x08000000

Screen usage:

1. screen /dev/ttyACM0 19200 (default baud for miosix serial is 19200)
2. To quit screen ctrl+A and D