Load subset of cases

[darothen]

Currently you can load specific, single cases via the .load() function. It would be useful to, say, subset one specific value for a given case but load all others. E.g., with the cases

emis = Case("emis", "Emissions Scenario", ['low', 'high'])
param = Case("param", "Tuning Parameter", ['x', 'y', 'z'])
other = Case("abc", "other factor", ['a', 'b', 'c'])

calling .load({var}, abc='a') would load the low/high and x/y/z cases but select along this last dimension. This would presumably speed up load times.