Restore operator T() on Field* and allow operator(*|->) on Ref/RefMut

[RaitoBezarius]

Fixes #133.

Each commit presents its rationale.

TL;DR:

• Add operator* and operator-> (const/non-const) for Ref/RefMut
• Add operator T() on FieldRef/FieldMut/FieldOwned using operator* on Ref/RefMut
• Added some regression testing for my usecases

[hkalbasi]

Thanks for the PR! I think adding a general propose T& operator*() is impossible due to layout deferences between C++ type and Rust type. What is possible is a T operator*() for Copy types (and the current implementation is UB for anything non trivial). Similarly, we can't have a normal -> operator and what we actually do is repeating all methods and fields of the T on Ref<T> too (which also helps in having . instead of -> which is more like Rust and C++ references). The field Copy implementation looks good to me.

[RaitoBezarius]

Thanks for the PR! I think adding a general propose T& operator*() is impossible due to layout deferences between C++ type and Rust type. What is possible is a T operator*() for Copy types (and the current implementation is UB for anything non trivial). Similarly, we can't have a normal -> operator and what we actually do is repeating all methods and fields of the T on Ref<T> too (which also helps in having . instead of -> which is more like Rust and C++ references). The field Copy implementation looks good to me.

I will drop the implementations and rework it accordingly, thanks.