User Roles: Manage the roles of users stored as bit masks

This class can manage the roles of users stored as bit masks.

It can load a PHP file that returns an array which defines the names of the roles that users may have.

A role is associated to a bit value. A complex role may be defined by an array that includes a list of other aggregated roles represented by a role bit mask.

The class can retrieve the bit mask of a role or change already defined roles.