[FEATURE] Improve handling of soundings with many points

[guidocioni]

I've been trying to read in high-resolution soundings form the DWD (german weather service) which can be found here https://opendata.dwd.de/climate_environment/CDC/observations_germany/radiosondes/high_resolution/recent/.
After converting to the right format Sharppy is able to handling them but
(1) it is really slow (loading the file takes more than 1 min)
(2) complains about non-monotonic height variable, although it is
I think most of these issues are due to the fact that Sharppy was not yet tested with such large input files.

I'm attaching the converted text file, ready to be read by Sharppy, in case someone wants to jump in.

sounding.txt