Avoid unecessary copies in (de)serialization

[Joseph Perez]

In serialization, when type checking is disabled, primitive types are passed through, so there is no unnecessary copies of primitive data.

However, copies could also be avoided with type checking, by doing the type checks and return the object as-is. Moreover, same thing could be done in deserialization. Concerning object deserialization, the deserialized dictionnary could be let untouched to be passed in object constructor.

This feature should be toogleable with settings keys. Should it be a key by operation or a single key? For now, I think two is better.