Assert, Exit builtins

* Builtins for assert and exit are added
* Tests for assert are added
* file operations from previous MR are added to documents
* assert and exit are added to documents

tests/test_lib_control.rs

@@ -2,6 +2,24 @@ mod control_lib_tests {
     use relish::ast::{eval, lex, SymTable};
     use relish::stdlib::{dynamic_stdlib, static_stdlib};
 
+    #[test]
+    fn test_assert_t() {
+        let document = "(assert true)";
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms);
+        dynamic_stdlib(&mut syms, None);
+        eval(&lex(&document.to_string()).unwrap(), &mut syms).unwrap();
+    }
+
+    #[test]
+    fn test_assert_f() {
+        let document = "(assert false)";
+        let mut syms = SymTable::new();
+        static_stdlib(&mut syms);
+        dynamic_stdlib(&mut syms, None);
+        assert!(eval(&lex(&document.to_string()).unwrap(), &mut syms).is_err())
+    }
+
     #[test]
     fn test_if_first_case_singlet() {
         let document = "(if true 1 2)";