Various documentation updates:

• Add some notes about general lib design, including modules
• Add a note about socket sharing done by the library, add an example how to perform updates in a loop
• Fix module & function links in the common api docs
• Show inherited members on apidocs for individual device classes
• Remove outdated documentation
• Add note about NTP
• Document onboarding process
• Add doc8 to CI
• Bump sphinx version to fix CI, related to [error occurred in build.] ImportError: cannot import name 'environmentfilter' from 'jinja2'  readthedocs/readthedocs.org#9038

Fixes #316
Fixes #257
Fixes #129