Add ASCAT data

Migrate TM/TMData/ASCAT.

In particular, use the following sources:

wget -r ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/MWF/L3/ASCAT/Daily/Netcdf/ * -r -np -nH --cut-dirs=7 -c
wget -r ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/MWF/L3/ASCAT/Daily/Doc/ * -r -np -nH --cut-dirs=7 -c
wget -r ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/MWF/L3/ASCAT/Monthly/Netcdf/ * -r -np -nH --cut-dirs=7 -c
wget -r ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/MWF/L3/ASCAT/Monthly/Doc/ * -r -np -nH --cut-dirs=7 -c
echo "Downloaded ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/MWF/L3/ASCAT on" > README
date >> README