Breaking changes

Initializing the class object now with ZACwire obj(int pin, int Sensor)
Non-espressif boards can read just one temperature sensor, as they can't pass a this-pointer to the ISR

Minor changes

removed template, as the IRAM can't be used with templates (see espressif/esp-idf#4542)
.begin() measures the bitWindow before attaching the interrupt, which is inspired by #14
the start-up is optimized, so directly 3ms after begin(), the first temperature value can be received
option for the ESP32 to pin the ISR to a specific core was removed for readibility. Measurements showed that the ISR just uses 0.078% of the CPU time, so that option had a neglectible effect
compatible with ESP8266 Arduino core 3.0.2