Add BMP280

[tyeth]

Closes adafruit/Wippersnapper_Components#135

There is a decision to be made about the sampling rates etc. The adafruit library has an example that states these to be the datasheet recommendataions, but the setSampling method has other defaults. As a result, for now, I have gone with the example parameters like so:

    // set up sampling as recommended in Adafruit library
    _bmp->setSampling(Adafruit_BMP280::MODE_NORMAL,  /* Operating Mode. */
                      Adafruit_BMP280::SAMPLING_X2,  /* Temp. oversampling */
                      Adafruit_BMP280::SAMPLING_X16, /* Pressure oversampling */
                      Adafruit_BMP280::FILTER_X16,   /* Filtering. */
                      Adafruit_BMP280::STANDBY_MS_500); /* Standby time. */

[brentru]

@tyeth I suggest to always use the default sampling modes as specified by the example, https://github.com/adafruit/Adafruit_BMP280_Library/blob/master/examples/bmp280test/bmp280test.ino#L49

[tyeth]

Tested with one sensor, using alternate address (bridged ADDR jumper), on qtpy-s2

[brentru]

@tyeth Could you resolve the conflict within library.properties?

[tyeth]

@tyeth Could you resolve the conflict within library.properties?

@brentru Resolved 👍

[brentru]

Looks good! We'll add the altitude unit to Adafruit_Sensor and revise this driver once it's added.