keyword tags

[delgadom]

keyword tags would be really nice.

If we structured our tags as a dictionary, with unnamed tags as _tag{i} and named tags having a name, you could search the values in the same way as we currently do, but also allow searching for key, value pairs, e.g.:

# returns reshaped, pop-weighted BCSD models
datafs search --variable=tas --weight=pop --probability=unweighted

which would enable distinguishing between this and

# returns gridded pattern models
datafs search --variable=tas --weight=unweighted --probability=SMME

Right now, you can't distinguish between types of "unweighted"