Changes the return types of a few functions to pass along a timestamp to blockTillConversionComplete
A few overloads are added to blockTillConversionComplete

Example usage:

sensors.setWaitForConversion(false);
DallasTemperature::result_t request = sensors.requestTemperatures();

sensors.blockTillConversionComplete(sensors.getResolution(), request);
or
sensors.blockTillConversionComplete(sensors.getResolution(), request.timestamp);