cd function

Signed-off-by: Ava Hahn <ava@sunnypup.io>

src/stl.rs

@@ -648,6 +648,17 @@ pub fn dynamic_stdlib(syms: &mut SymTable, shell: Option<Rc<RefCell<posix::Shell
 
         if posix_cfg_user_form {
             posix::load_posix_shell(syms, shell_state);
+            syms.insert(
+                "cd".to_string(),
+                Symbol {
+                    name: String::from("cd"),
+                    args: Args::Strict(vec![Type::String]),
+                    conditional_branches: false,
+                    docs: posix::CD_DOCSTRING.to_string(),
+                    value: ValueType::Internal(Rc::new(posix::cd_callback)),
+                    ..Default::default()
+                },
+            );
         }
     }