This library uses ctype_alpha() function in two places.

1. If I'm not wrong this function is locale dependent and I don't see any setlocale() calls. So, would be better to have something that does not depend on locale.
2. If we got rid of this function use the library would not need Ctype extension which is not always installed by default.

I think it should be easy to replace this function with something based on ord() or str[c]spn().