Reintroduced the _filter_visitor_factory and _order_visitor_factory
methods so that derived Aggregate classes can customize.
Changed the way the ConstantGroup class is defined to make pylint v. 1.x
happy.
Added a "quote" flag to the resource_to_url utility function and
replaced single quotes in linked entities in CQL strings with double
quotes.
Added links options processing functionality.
Renamed the new dynamic attribute configuration feature from "links" to
"refs" and introduced a "ref" directive.
Renamed the new dynamic attribute configuration feature from "links" to

"refs" and introduced a "ref" directive.
Added forgotten zcml file.
Merge branch 'master' of https://github.com/cenix/everest