* Enable to stack Batch instances. Add Batch cat static method. Rename cat in cat_ since inplace.
* Properly handle Batch init using np.array of dict.
* WIP
* Get rid of metadata.
* Update UT. Replace cat by cat_ everywhere.
* Do not sort Batch keys anymore for efficiency. Add items method.
* Fix cat copy issue.
* Add unit test to chack cat and stack methods.
* Remove used import.
* Fix linter issues.
* Fix unit tests.
Co-authored-by: Alexis Duburcq <alexis.duburcq@wandercraft.eu>
ec270759ab