feat: Add parsing support for primitive types.

src/main.rs

@@ -5,7 +5,7 @@ pub mod parser;
 pub mod token;
 
 fn main() {
-    let mut parser = Parser::new("break;");
+    let mut parser = Parser::new("{ let return_code: i32 = 12; return return_code; }");
 
     println!("{:#?}", parser.parse_statement());
 }