Enable compositing several quantities on the command line

[andershenja]

The composite generator can composite multiple quantities, e.g. TH and DBZH simultaneously for the same product. However, this feature is not available on the command line, using 'radarcomp'.

Doing this would involve tweaking two files:
bin/radarcomp, almost at the bottom:
if ',' in options.quantity: options.quantity = options.quantity.split(',')

and with updated documentation for options.quantity.

and Lib/compositing.py, in the _generate method:

if type(self.quantity) == types.ListType?:
for q in self.quantity:
generator.addParameter(q.upper(), self.gain, self.offset)
else:
generator.addParameter(self.quantity, self.gain, self.offset)

and importing the types module.

This approach only makes sense when compositing quantities that share the same gain and offset, probably also nodata and undetect.