allowing namespaces containing Spec like Specification (fix #5)

I'm not sure this is the most elegant solution but I couldn't use any preg_replace because it made specs fail. Couldn't figure out why.
So i switched back to some good old str_replace.

From what I understand, Spec has to be replaced in 2 cases : 

- When it is the configured Spec subnamespace
- When it is at the end of the classname (indicating that the class indeed is a spec)

Every other occurence should be left untouched