Arduino-OBD2-Async

Based on stanleyhuangyc/ArduinoOBD, with asynchronous data requesting.

There are new functions:

    void asyncRequest(byte pid); // send request for specific PID
    bool asyncInProgress();      // check that we already are waiting for response
    bool asyncGet(int& result);  // try to get response into 'result'

Typical usage:

    if (!obd.asyncInProgress())
        obd.asyncRequest(PID_RPM);
    int response = 0;
    if (obd.asyncGet(response))
        Serial.println(response);