Simple scopes.

Scopes can be defined similar to a where, like:

User::scope("first_level",array("level"=>1));
$users = User::first_level();

A very important point here is that they need to be called as methods (like
static methods, like above). Trying to call them as attributes, like

User::first_level

won't work because that way they seems to be class constants.

Chained scopes will come. Just need to send a already created builder to
Collection methods.