Add public API to parse calibration data

[pawelszramowski]

bme280_parse_temp_press_calib_data and bme280_parse_humidity_calib_data functions are extracted from internal API to accompany existing bme280_parse_sensor_data and bme280_compensate_data in order to allow processing data gathered outside the driver.

This is useful for applications which do not find API based on struct bme280_dev suitable and would rather communicate with the sensor on their own.