Added directfs

Added a very rudimentary file I/O system suitable for experimenting
with the language further. A better one will be designed when we have
sensible error management.

src/interner/mod.rs

@@ -5,9 +5,7 @@
 mod monotype;
 mod multitype;
 mod token;
-// mod traits;
 
 pub use monotype::TypedInterner;
 pub use multitype::Interner;
 pub use token::Tok;
-// pub use traits::{DisplayBundle, InternedDisplay, InternedInto};