Tk::Role::Dialog is meant to be used as a Moose
role to be composed for easy Tk dialogs creation.

It will create a new toplevel with a title, and possibly a header as well
as some buttons.

The attributes (see below) can be either defined as defaults using the
'_build_attr()' methods, or passed arguments to the constructor call. The
only mandatory attribute is 'parent', but you'd better provide some other
attributes if you want your dialog to be somehow usable! :-)