feat(core): add load and include prelude

src/bin/lisp_demo.rs

@@ -15,6 +15,8 @@ fn main() {
         "(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))",
+        "(load \"(defun loaded-foo (x) (+ x 1))\")",
+        "(loaded-foo 1)",
     ];
 
     let environment = Environment::default();