feat(prelude): add progn

src/bin/demo.rs

@@ -15,6 +15,7 @@ fn main() {
         "(let '((a . (vec3 1 2 3)) (b . (vec3 4 5 6))) (vec3-dot (vec3-norm (vec3-add a b)) a))",
         "(defun do-n-times (f n) (if (= n 0) '() (cons (f) (do-n-times f (- n 1)))))",
         "(do-n-times (lambda () (print 'hello)) 5)",
+        "(progn (print 'hello) (print 'world))",
     ];
 
     let environment = Environment::default();