Possibility to specify an interface for the binding to be mapped to

There is a problem when working with bindings and specific interfaces, if a more generic interface is specified in the handler after the binding, the values of the passed object are zero since the context does not know how to map to that interface.

This PR aims at solving this by making it possible to optionally specify an interface pointer as the second argument of the binding main functions and thus allowing the context to be aware of the interface when mapping.

What do you think?