Hit detection

[David-Estevez]

Enable hit detection with current sensor input (VCC/2 offset -> #16 ).

[David-Estevez]

Now that #16 has been solved, this issue can be simply solved by adjusting the thresholds.

Nevertheless, I have observed that the sensor detection (checking wether the piezo is present or not) affects the hit detection, as the microcontroller is busy checking for too long, and some hits are not detected if they are synced with the checking. This second part requires further testing.