Altitude in gps should be in meter and not in cm

[cpihl]

Betaflight blackbox logs altitude in cm from gps and barometer, and this is exported as integer to gpx file field (ele), while comment in gpxwriter.c says "Altitude is in meters".
The standard unit for altitude in gpx file is meter, for example used by google earth viewer.
I also added a flag alt-offset to enable adjustment of altitude, if anyone interested.

[mikeller]

@cpihl: Yes, please open a pull request to fix this.

[stale]

This issue / pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs within a week.

[stale]

Automatically closing as inactive.

[HereticToXa]

Why is it closed? The problem is still there