Add new humidity/temperature sensor HTU21D.
Add unittest code for MPL115A2.
Add unittest code for MPL115A2.
Add dummy test case for HTU21D.
Add method to calculate CRC correspoinding to the specified value with bit length.
Implement getCelsius and getHumidity.
Remove unneeded code.
Fix humidity unit.
Fix family definition.
Merge htu21d branch.
Support temperature/humidity sensor HTU21D.