* Prepare for LoRa mode
* Initialization of LoRa mode
* Partial impl. of LoRa mode
- writing/reading packet missing
* TX and RX in LoRa mode initially working
* Read RSSI and CRC, 62.5 kHz/SF 9, refactoring, README.md
* Clear 'TxDone' interrupt before going to Tx mode
* Update README.md
* LoRa mode has no address filtering (for now)
* Test FSK + small change in DIO4/timeout interrupt handling
- if DIO4 mapping is 00, an interrupt occurs while setting rx mode,
  which seems to break/hang SPI communication