read_RWS

This function gives the datenum 'time' and the matrix 'M' of the
radiosoundings read in the input file, obtained as ascii text by
'cut and paste' from 'http://weather.uwyo.edu/upperair/sounding.html'.
The input file can contain an arbitrary number of radiosoundings.
The 'station_id' is the number of the station, required to locate the
beginning of each data block. It must be in string format.
If station_id is not defined, it is read from the first line of the text file,
so ensure that the first line contains the ID in the first five characters.
"M" has three dimensions:
1. Vertical measurements of every radiosounding (50 rows)
2. Columns of the different quantities (11 columns):
PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV
hPa m C C % g/kg deg knot K K K

3. Number of radiosoundings in the input file (variable).
"time" is the vector of datenum of each radiosounding, as read from the file.
This variable has the dimension of the third dimension of M.

Created by Federico Angelini, ISAC-CNR
30 Oct 2009