elif instead of if, avoiding an extra test.
Using netCDF4.date2num to handle date limits.
AVISO_download now parse -D into a datetime object.
Minor upgrade. AVISO_download wasn't working with date bounds.
Bugfix #3, fixed issue when area includes Greenwich.

The output is as requested. 10:350 will return almost all the globe,
while 350:10 will return a 20 degrees range, from 350 to 10,
including Greenwich.