Merge: Serialization support SimpleCollection and Map, also bug fixes

This PR is the result of using Nit serialization to implement game saving/loading in WBTW.

Update the serialization to work with (or avoid) the new auto constructors.

Support serializing Sets and Maps.

The `is_same_serialized` fix a problem where two instances were wrongly serialized as being the same. Because it previously used a `HashMap` (and thus `==`), two different _empty_ arrays were serialized as one and resulted in a single object on deserialization.

Once this and #1348 are merge, I'll update the calculator example to use the serialization.

Pull-Request: #1352
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>