Release v0.20.1 - Githubissues

Update README, etc. See delta in #123 for details.

[x] update library.properties version to 0.20.1
[x] update CATENA_ARDUINO_PLATFORM_VERSION in CatenaBase: change here: https://github.com/mcci-catena/Catena-Arduino-Platform/blob/f9167f397566aa4c22d8c5dae4ffd11317ae8c00/src/CatenaBase.h#L58
[x] update README.md version for badges (line 7)
[x] update README.md release history (towards end).
[x] generate pull request
[x] merge into master.
[x] tag and release.

mcci-catena / Catena-Arduino-Platform