K360 docs, Improved solaar-cli argparse fix

This pull includes an improved fix for the `-D` argument and includes information about the K360.

I took the moment to add reprogrammable keys to the features list in devices.md, please update it accordingly with your own devices.

The k360.txt file also includes output from ltunify about the receiver. The ltunify output is based on ltunify v0.1-27-gb493f9b, see its hidpp20.c source code for more names for certain feature IDs. The solaar-cli output is annotated with information about the keys.