0.6.1 - add missing classes to doxygen docs

• 0.6.1
  • Create a second Jenkins continuous build pipeline file
    tests/JenskinfileUnitHost to use UnitHostDuino to run the unit tests
    natively on Linux. The entire set of unit tests builds and runs in 20
    seconds under UnixHostduino, compared to about 8 minutes for the single
    Nano environemnt, and 32 minutes against 4 boards (Nano, ESP8266, ESP32,
    SAMD21).
  • Fix Doxygen PREPROCESSOR so that it picks up classes which are enabled
    only on some environments (e.g. ESP8266, ESP32).
  • Add circuit schematics to OledClock and WorldClock examples.
  • Simplify logging::printf() used internally for debugging.
  • No functional change from 0.6.