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- Add aggregation option 'current' to volume and intercepted_volume.
- Using a non-tuple sequence for multidimensional indexing is deprecated; use
`arr[tuple(seq)]` instead of `arr[seq]`.
- Properties should be strings so we can use string methods on them.
- Do not prepare levees if there aren't any.
- Split requirements file to allow for finer grained builds (for instance to
generate the documentation).
- Add 'intercepted_volume' to NodesAggregateResultsMixin.
- Split requirements file to allow for finer grained builds (for instance to
generate the documentation).