Missing .printf method

[eigen-value]

Serial.printf calls don't compile since Monitor is missing such a method.

reproduce:

• Open Arduino IDE and run the WireScan example on the UNO Q

This issue is probably related to #69

[per1234]

Note that printf has historically been intentionally excluded from the Print class API. It is true that it has been implemented in some 3rd party cores, but those cores are deviating from the formal Arduino core API.

Note that inconsistent implementation of printf is harmful because it results in the loss of the portability that has been the hallmark of the Arduino core API. If it is to be implemented, that should be done universally rather than sporadically. There is a proposal for addition of printf to the official Print class here:

arduino/ArduinoCore-API#28

An explanation for why Arduino has historically officially rejected the addition is linked to from that thread.