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Fixes
* Fix link by not setting constraints that limit direction `38 <https://github.com/oemof/oemof-tabular/pull/38>`_
* Fix storage investment `33 <https://github.com/oemof/oemof-tabular/pull/33>`_
* Link investment `28 <https://github.com/oemof/oemof-tabular/pull/28>`_
* Variable cost `24 <https://github.com/oemof/oemof-tabular/pull/24>`_
* Marginal cost `23 <https://github.com/oemof/oemof-tabular/pull/23>`_
Features
* Adjust to new oemof.solph structure `21 <https://github.com/oemof/oemof-tabular/pull/21>`_
* Allow to define custom foreign keys `39 <https://github.com/oemof/oemof-tabular/pull/39>`_
* Add constraint tests for most facades `35 <https://github.com/oemof/oemof-tabular/pull/35>`_, `#42 <https://github.com/oemof/oemof-tabular/pull/42>`_
* Reduce number of imported packages `32 <https://github.com/oemof/oemof-tabular/pull/32>`_, `#49 <https://github.com/oemof/oemof-tabular/pull/49>`_
* Cleaned up the badges in README `59 <https://github.com/oemof/oemof-tabular/pull/59>`_
* Move most CI services to github actions `37 <https://github.com/oemof/oemof-tabular/pull/37>`_