Converted Interner to work with Rc-s

- Interner no longer contains unsafe code
- Tokens now hold a reference to the value they represent directly

This will enable many future improvements

src/interner/mod.rs

@@ -5,9 +5,9 @@
 mod monotype;
 mod multitype;
 mod token;
-mod traits;
+// mod traits;
 
 pub use monotype::TypedInterner;
 pub use multitype::Interner;
 pub use token::Tok;
-pub use traits::{DisplayBundle, InternedDisplay, InternedInto};
+// pub use traits::{DisplayBundle, InternedDisplay, InternedInto};