conlang: PATTERN MATCHING AND DESTRUCTURED BINDINGS WOOOOO

- Integrate the Match and Pattern nodes into the AST
  - TODO: `let x: T` is ambiguous with `let x: {}`. Currently the latter takes precedence in the parser.

- Implement pattern matching through unification in the interpreter.
  - It's not fast, but it works!

- Refactor destructuring assignments to use the new pattern functionality

compiler/cl-parser/src/error.rs

@@ -119,6 +119,10 @@ pub enum Parsing {
     Break,
     Return,
     Continue,
+
+    Pattern,
+    Match,
+    MatchArm,
 }
 
 impl Display for Error {
@@ -225,6 +229,10 @@ impl Display for Parsing {
             Parsing::Break => "a break expression",
             Parsing::Return => "a return expression",
             Parsing::Continue => "a continue expression",
+
+            Parsing::Pattern => "a pattern",
+            Parsing::Match => "a match expression",
+            Parsing::MatchArm => "a match arm",
         }
         .fmt(f)
     }