Explicit coordinate labels

[kilojoules]

It could be useful to let the user know if oneof wind resource variables, e.g. wind_speed, are coordinates or data variables.

Instead of this:

if type(ws) == dict:
   # its a data var
elif type(ws) == list:
   # its a coordinate
else: 
   # we're not sure

Have a field that says "I am a coordinate"

[SchmJo]

This would actually be very useful for any of the optional choices throughout the complete schema, since sometimes the data based checking might be painful for users. Also, during schema checking it should all be decided already, and re-doing this on the user side potentially adds errors