[geolocation-sensor] Barometer altitude (if the device has barometer) (#43)

karianpour has just created a new issue for https://github.com/w3c/geolocation-sensor:

== Barometer altitude (if the device has barometer) ==
I wish that this API could provide barometric altitude as well. The use case is for sport activity when we need precise altitude data in the track log, where the GPS altitude is accurate but not precise.

Please view or discuss this issue at https://github.com/w3c/geolocation-sensor/issues/43 using your GitHub account