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Renamed ``compass.api.utility`` to ``compass.api.util`` for consistency with
``compass-interface-core``.
Moved http error handling to ``compass.api.util.http_errors``.
Updated pin on ``compass-interface-core`` to ``0.14.1``.
Added ``compass/api/resources/hierarchy_flat.json`` and
``compass.api.util.flatten_units``.
Added initial hierarchy API endpoints.