Unsafe Deref Trait

I often make newtypes around raw pointers, and enabling the same Deref functionality that exists with raw pointers and refernces would go a long way towards making these wrappers more ergonomic. Today though, there's really no way to do that in Rust, which means that newtypes over raw pointers are kind of gimped.

My proposal is basically to a copy-paste Deref and DerefMut, and make them unsafe traits that work on raw pointers.

For reference, here is a different proposal that partly addresses the same ergonomic problem: Need for -> operator for Unsafe Code Guidelines