fixed some compiler warnings

added equality checks to sensor-data classes
more robust sensor reader [fixed some issues]
added support for gps
added support for compass
added sensor-data-writer
added test-cases
minor changes

sensors/pressure/BarometerData.h

@@ -13,6 +13,19 @@ struct BarometerData {
 
 	explicit BarometerData(const float hPa) : hPa(hPa) {;}
 
+	/** valid data? */
+	bool isValid() const {
+		return hPa == hPa;
+	}
+
+	bool operator == (const BarometerData& o ) const {
+		return EQ_OR_NAN(hPa, o.hPa);
+	}
+
+private:
+
+	static inline bool EQ_OR_NAN(const float a, const float b) {return (a==b) || ( (a!=a) && (b!=b) );}
+
 };
 
 #endif // BAROMETERDATA_H