How should we handle the altitude grid boundaries?

after discussion with @marbsrednas it would be good to add comments to the altitude and altitude_bnds variables clearly stating which altitude they refer to:

• altitude is the internal RT grid used by SCIATRAN
• altitude_bnds are the layer interfaces as SCIATRAN interprets them

Specifically, it should be clear to the user that, e.g. in case of BAMF, the BAMF is not the effective value for altitude.