New standard proposal

[rbran]

This is an proposal to standardize the inner-workings of the API, specially with the FFI types.

Mostly it consist of creating standard functions to create/manger FFI wrapper types, such as functions into_raw, as_raw, from_raw, ref_from_raw, the use of NonNull<T> instead of the naked pointer, hide inner representations, etc.

This don't necessarily has the objective of being merged, but act like a guide to new implementations.