Add EvalPackage.

src/packages/eval.rs

@@ -0,0 +1,12 @@
+use crate::def_package;
+use crate::module::FuncReturn;
+use crate::stdlib::string::String;
+
+def_package!(crate:EvalPackage:"Disable 'eval'.", lib, {
+    lib.set_fn_1_mut(
+        "eval",
+        |_: &mut String| -> FuncReturn<()> {
+            Err("eval is evil!".into())
+        },
+    );
+});