conlang: Unify binding operations!

This breaks out the pattern matching/unification algorithm from cl-interpret/interpret.rs to cl-interpret/pattern.rs

TODO: pattern destructuring in const, static :^)

compiler/cl-ast/src/ast.rs

@@ -153,7 +153,7 @@ pub struct Function {
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Param {
     pub mutability: Mutability,
-    pub name: Sym,
+    pub bind: Pattern,
 }
 
 /// A user-defined product type