Trying to improve what's already great

Hi !

Mostly, I tried to simplify the way Application.php was written by reducing the nesting of if/else structures.
Also, adding a preliminary test for the url allows us to optionnally redirects to a 404 in the controller test, which seems to me useful.

The commit about Nginx speaks for himself, and while not being necessary, it adds a notice about not only adding a redirecting directive for the main location block but also for the .php one. This last point matters : without it, asking for a .php file that can't be found by nginx will likely result in a 'No input file specified' error.

By the way, thank you very much for PHP-MVC. I've been studying it for some days now and it has been very interesting !

Erwan