Add raw API for custom syntax.

src/api.rs

@@ -164,14 +164,8 @@ impl Engine {
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
     pub fn register_type_with_name<T: Variant + Clone>(&mut self, name: &str) -> &mut Self {
-        if self.type_names.is_none() {
-            self.type_names = Some(Default::default());
-        }
         // Add the pretty-print type name into the map
-        self.type_names
-            .as_mut()
-            .unwrap()
-            .insert(type_name::<T>().into(), name.into());
+        self.type_names.insert(type_name::<T>().into(), name.into());
         self
     }