Release v0.6.0

[terrillmoore]

It's time for v0.6.0.

• [x] update version in header file: https://github.com/mcci-catena/arduino-lorawan/blob/2ea816b7a8f70813e07c1da81c0f769149b7665f/src/Arduino_LoRaWAN.h#L32
• [x] update library.properties
• [x] update library.json
• [x] update VERSION.txt
• [x] update README.md
  • [x] the badges at the front
  • [x] the change history/release notes
• [x] create pull request
• [x] merge
• [x] tag