conlang: add lang items, remove Empty, and shuffle typeck

stdlib/std/never.cl

@@ -0,0 +1,4 @@
+//! Never: the return type of an infinite loop
+
+#[lang = "never"]
+type Never = !;

stdlib/std/option.cl

@@ -1,6 +1,7 @@
 //! The optional type, representing the presence or absence of a thing.
 use super::preamble::*;
 
+#[lang = "option"]
 pub enum Option<T> {
     Some(T),
     None,

stdlib/std/result.cl

@@ -1,6 +1,7 @@
 //! The Result type, indicating a fallible operation.
 use super::preamble::*;
 
+#[lang = "result"]
 pub enum Result<T, E> {
     Ok(T),
     Err(E),