Extend events to include Fan Tacho

[T3P3]

Currently deamon.g needs to be used to monitor fan tacho inputs and take appropriate action if the tacho is outside of the required range.

The feature request proposes adding a tacho-error.g and associated event which works in a similar manner to other events (the D parameter is the fan number, the P parameter could optionally be too high or too low, the default action could be "do nothing" for backward compatibility).

This would require extending M106 or creating a new gcode command to set a expected tacho value and an acceptable range +/-% of that value outside of which a warning was raised.

To handle 4 wire fans it may be necessary to add a scaling factor.