Firmware for the BT_DAC project.

This Firmware is configured for v.1.2 (Schulius Edition)

Changes from v.1.0

• WS2812b LED-strip support
• button actually wired and not just connected to hardware-reset
• battery voltage sensing
• charging state sensing
• pin remapping
• that's about it

TODO

• add pin for sensing 5V presence
  • add CONNECTED_CHARGING and CONNECTED_NOT_CHARGING as battery states
  • improve battery state detection
  • dont go to sleep when 5V is connected
• change button to pullup
• move capacitor to work with 3.3V, not V_BAT, currently it messes with the charging chip's no_bat detection
• use ext0 wakeup for headphone connector
• use ext1 for 5V presence or button press
• add some hardware pullups / pulldowns
• maybe add button debouncing
• battery level reporting
• led strip stuff :
  • countdown display for no pogo connector
  • show when connected
  • fix that startup bug