Openfisca-core

* Fix `dtype` attribute for `EnumArray`s (returned when calculating a variable of `value_type` `Enum`):
- It was the type `numpy.int16` and not the dtype instance `numpy.dtype(numpy.int16)`
- This caused issue when trying to export an `EnumArray` with `pandas`

* Fix operators such as `household.first_parent`, `foyer_fiscal.declarant_principal` for multi-entities simulations.
- This issue was not affecting simulations with several persons in a _single_ entity
- The underlying `entity.value_from_person` operator was not working as expected in case the persons of the simulation were not sorted by entity id in the persons vector (see example in 22.0.8 right below).

* Fix `entity.max`, `entity.min`, `entity.all` and `entity.reduce` for multi-entities simulations.
- This issue was not affecting simulations with several persons in a _single_ entity
- These operators were not working as expected in case the persons of the simulation were not sorted by entity id in the persons vector. For instance:
- First household: [Alice, Bob]
- Second household: [Cesar]
- Persons vector: [Alice, Cesar, Bob]

* Update CircleCI configuration to its v2

* Improve parameters performances

* Update country-template dependency to >= 3.0.0, < 4.0.0