Add altitude

[caternuson]

Add an altitude property to return pressure based altitude in meters. Ref BMP280 implementation:
https://github.com/adafruit/Adafruit_CircuitPython_BMP280/blob/f65303074498e07db883e73c067a8b9e491451a2/adafruit_bmp280.py#L355

[caternuson]

Don't we want it here also?

[ladyada]

oops sorry thought this was the arduino one - i dont think we do altitude calc in the library, only examples?

[caternuson]

The CircuitPython BMP280 lib has it? Simple PR FWIW. Not much more than a copy pasta from the BMP280 lib.

[ladyada]

we'd rather have it as an example instead of API addition

[caternuson]

@ladyada I left the PR open while being gone for a few days. It looks like it got merged and released. Want me to revert to remove and make a new release?

[ladyada]

nah its ok!