Document the Move Semantics in the Bindings

The Bindings can easily be misused (less so where we have garbage collector integration) and cause segfaults if you don't know about the Ref / RefMut / (none) postfixes of the types. Therefore this should very clearly be documented so you don't miss it.

Start with the Bindings entry points and trace how the Ref, RefMut, and no-postfix type forms are exposed. Document the move semantics and the misuse cases that can cause segfaults, with wording clear enough that users do not overlook the distinction.

Written by the indexing model from the issue text.