v0003 (2016.01.25):
 * 10K resistor has been removed - replaced by the internal pull-up;
 * minor PCB modifications.
v0002 (2015.10.22):
 * new modes has been added;
 * increased sensitivity.
v0001 (2015.09.11):
 * additional mode;
 * code optimization.
v0000 (2015.07.28):
 * first release.