Allow multiple locations

[woodcoder]

A single location can be specified for finding the lowest carbon intensity.

However, some tasks will involve multiple locations (e.g. database or webserver in a different region) -- therefore it would be good to be able to specify multiple locations on the command line.

Either replacing any default location, or in addition to the default.

This will involve working out when the best overlapping time would be - and might also need some sort of percentage weighting to be specified too, to take into account asymmetric processing.