* Enable a 'link' attribute on collections for use in serializations.
1.2.39
* Allow subclassing of Bag, Recipe, Tiddler and User entities.
1.2.38
* More robust handling of bag permissons in JSON serialization.
1.2.37
* Add support for special_bag_detectors.
1.2.36
* 400 on bad base64 input in JSON PUT of tiddler. * Trap NoBagError when listing tiddler revisions. * Handle lack of Content-Length on POST as 400 not 500.