FR: better event detection via dual moving average cross-over

[Andrei-Pozolotin]

1. currently "tare" happens once, on setup:
   https://github.com/IvDm/Z-probe-on-smd-resistors-2512/blob/master/strain_gage_switch_ATtiny85.ino

2. this does not reflect environment changes during long operation:

• parameters temperature drift,
• parameters mechanical creep,
  etc.

3. a better way is to use dual moving average cross-over approach,
   and eliminate dependency on environment changes i.e.:

// detect touch events
void process_trigger() {
    const int32_t fast = moving_fast.average();
    const int32_t slow = moving_slow.average();
    const int32_t delta = fast - slow;
    if (delta > 0) {  // react only on proper direction
        if (has_trigger) {
            if (delta < DELTA_PASSIVE) {  // detect turn off
                has_trigger = false;  // remember state
                moving_slow.setup(trigger_slow);  // recover to event start
                process_output (LOW);  // issue turn off
                time_passive = millis();  // report event finish
            }
        } else {
            if (delta > DELTA_ACTIVE) {  // detect turn on
                has_trigger = true;  // remember state
                trigger_slow = slow;  // remember till event finish
                process_output (HIGH);  // issue turn on
                time_active = millis();  // report event start
            }
        }
    }
}

4. here is full sketch for arduino/nano:
   https://gist.github.com/Andrei-Pozolotin/e7bf413e2438863a04c2497258662bec