add readPandT( ...) to library allowing much better bandwidth performance

[misc-protolabs]

my local change to the library which appears to be fully operational:

//
/*!
@brief Performs a reading and returns the ambient pressure and temperature.
*/
//
void Adafruit_BMP3XX::readPandT( float* press, float* temp) {
performReading();
*press = pressure;
*temp = temperature;
}