Enhancement: expose spreading factor, coding rate, signal bandwidth, CRC check

[applio]

I suggest adding the ability to control spreading factor, coding rate, signal bandwidth, and perform CRC checks on inbound packets. These features are sadly absent from the venerable RadioHead library implementation which heavily inspired the current implementation of this module but these features are available in the hardware of the Adafruit RFM95W (and close cousins) and through the software of other libraries such as https://github.com/MZachmann/LightLora_Arduino or https://github.com/MZachmann/LightLora_MicroPython .

As it is, the current implementation only supports fixed values for these controls but to make good use of the RFM9x hardware, to achieve good LoRa performance over long distances under non-ideal (real) conditions, the ability to modify these settings is rather important.

When dealing with the real world, noise can cause data corruption and the hardware's ability to perform CRC checks on packets becomes especially useful. For this reason, enabling the detection of corruption through hardware-based CRC checking is also proposed.

I have a patch to offer the above functionality that may be worth considering. It retains the current default behavior while offering the ability to change these settings at the time of instantiation of the RFM9x class.

[brentru]

Thank you for adding these features!

Addressed in #21 and released in in 1.1.5, closing!