replaced callback in camelCaseToDelimiter with strtolower

Hi!

The `create_function` version of `camelCaseToDelimiter` can be used to inject arbitrary code via the `$delimiter` parameter (set it to `' . printf("hello") . '` for example). I'm not sure if you expose that parameter to the outside world somewhere, but I think it's still better to not have that in the code. :)