BOOTLOADER BUGFIX: USART electrical coupling happens if there is no PULL-UP resistor. Without this, a bootloader bug manifests itself as a sent handshake being received on the same UART and trappedin the receive_handshake_callback
Merge pull request #1 from njoubert/bootloader-uart-fix

BOOTLOADER BUGFIX: USART electrical coupling happens if there is no PULLUP resistor. Without this, a bootloader bug manifests itself as a sent handshake being received on the same UART and gets trapped in the receive_handshake_callback.