* Change _delay_ms/us() to wait_ms/us()
* Switch to platform-agnostic GPIO macros
* Add AVR spi_master and migrate Adafruit BLE code
* Set verbose back to false
* Add clock divisor, bit order and SPI mode configuration for init
* Add start and stop functions
* Move configuration of mode, endianness and speed to `spi_start()`
* Some breaks here would be good
* Default Adafruit BLE clock divisor to 4 (2MHz on the Feather 32U4)
* Remove mode and divisor enums
* Add some docs
* No hr at EOF
* Add links in sidebar
