Updated db.c

- Added "CREATE TABLE IF NOT EXIST" into db.c initializeDatabase()
- Moved database file to a static location: /var/local/auriol-db.sl3
- Simplified some variable names and function name (saveAnemometerTemperatureAndHumidity -> saveTemperature)
- Added saveHumidity function and database table
- Entered individual exit codes for errors
- Added a comment with an Excel calculation of average Wind Speed and Direction

I am currently working on implementing a function saveWind(float speed, float gust, unsigned int direction ) based on the above mentioned Excel calculation. My idea is to save an average wind speed, maximum wind gust and average wind direction (wind strength taken into account) based on every 10th reading.  

Unfortunately my aneometer  is not responding (frozen batteries?) so I can not verify the code.