Really nice! The template system is small but still efficient...

Really nice! The template system is small but still efficient, you can tell that you thought this through. Although one thing I would like to note for you.

Instead of defining a directory separator you can just use '/' since it works on both *nix and Windows.

Also, generally when writing MVC applications and I come to the settings part, now this way you're doing it works. But it would be way more comprehensive to use the default PHP INI system and use parse_ini_file on this instead into a multi dimensional array.