set kmsl = 1 in order to interpret receptor points in mASL instead of mAGL

[FriedrichKlappenbach]

According to hysplit documentation and a question here:
https://hysplitbbs.arl.noaa.gov/viewtopic.php?t=1175

one can set the kmsl=1 in run_stilt.r

This allows to calculate the line-of sight relative to mean sea level (msl) instead of surface level (asl). This is especially important if the line of sight moves over uneven terrain.

major change in generate-receptors.r is needed in this case.