Fix telemetry altitude.

Frsky assumes a positive after-decimal uint16.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Telemetry: Send opentx variometer values.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Merge pull request #19 from the-kenny/master

Telemetry additions