Release 0.7.0

[terrillmoore]

It's time for v0.7.0. But note that we must release Arduino-LMIC first since we will be pulling it in automatically on the newer IDE.

• [x] update version in header file around line 32.
• [x] update library.properties
• [x] update library.json
• [ ] ~update VERSION.txt~
• [ ] update README.md
  • [x] the badges at the front
  • [x] the change history/release notes
• [ ] create pull request
• [ ] merge
• [ ] tag