Mail class (v2.6) : to() method accepts arrays

Mail::to() method can now both be used for one or more addressees
Response : use call_user_func instead of $execute
Response headers : disable cache on SYSTEM_DEBUG
Index : bug fix not found controller $name
Request : bug fix request URI definition
Implement Image class library (v1.0)

Allow image treatments such as rotation, resize (with options), and
also allow image conversion