 - double check footprints for small caps
   - amp 2.2uF (is this in the bom?)
   - USB IC xtal
   - battery voltage divider cap
   - usb IC power (didnt the app notes call for smaller sizes?)
 - fix amp footprint/package discrepancy
 - gpio connector needs NPTH
 - esp32 xtal footprint is too small
 - usb power mosfet has incorrect pinning
 - uart rx/tx swapped
 - add button to EN pin(?)
 - pull IO0 down during boot to flash
   - use IO2 for SDA instead, then add a BOOT button?
 - need p channel mosfets for most switches :(
 - tie 3v3 reg mode to a gpio
 - replace analog ldo with filtering caps for high noise
 - ESP32 only support to set GPIO0/GPIO1/GPIO3 as mclk signal
 - add real pullups to everything i reckon
