Made AreaId encodable and sortable

[stan-at-work]

This PR fixes this issue.

[stan-at-work]

Any updates on this ?

[caduandrade]

Hi @stan-at-work!

A few points:

1. I think _AreaId should not receive an id, because if there is an id, _AreaId would not even be instantiated. This class represents an automatically generated or undefined id. Perhaps the name could be _AreaUndefinedId.

2. This change does not make Area encodable, only _AreaId. Right? I believe the Area will not be possible to do it automatically because it receives functions as parameters. In this case, perhaps the solution is to have a (static?) registry to map functions with some identifier. The toJson method could replace the function with its identifier. The fromJson method could obtain the correct function from the registry given the identifier. Anyone using the API could map their functions to this registry.

What do you think? Does that make sense?

[stan-at-work]

Hey ✋

1: Yes and no... I like to give people the freedom to pass their own parameters to objects if possible.
I think it does no harm if you can pass them in. This way, we give others the freedom and are not limited to one implementation.

2: Correct, this only makes _AreaId encodable, not Area.
You can manually make Area encodable, so that's not necessary.

[stan-at-work]

@caduandrade Hello ?