merge hysplitdev back into develop.
Addresses issues #102 adding function to hytraj to combine several tdump files into one dataframe.
Addresses issue #103 add some unit testing for hysplit.py and hytraj.py
Small changes to hysplit.py functions
get_latlongrid improved exception statements
get_latlon replace x>=180 test with x>=180+lon_tolerance
get_thickness modified to calculate if attribute specifying vertical
levels is bad.
merge hysplitdev back into develop. Addresses issues #102 adding function to hytraj to combine several tdump files into one dataframe. Addresses issue #103 add some unit testing for hysplit.py and hytraj.py Small changes to hysplit.py functions get_latlongrid improved exception statements get_latlon replace x>=180 test with x>=180+lon_tolerance get_thickness modified to calculate if attribute specifying vertical levels is bad.