Fix feature builds.

src/engine_api.rs

@@ -9,7 +9,7 @@ use crate::stdlib::{
     any::{type_name, TypeId},
     boxed::Box,
     format,
-    string::String,
+    string::{String, ToString},
     vec::Vec,
 };
 use crate::{

tests/functions.rs

@@ -51,6 +51,7 @@ fn test_functions() -> Result<(), Box<EvalAltResult>> {
     Ok(())
 }
 
+#[cfg(not(feature = "no_module"))]
 #[test]
 fn test_functions_context() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();