Add some comments to the tag module controllers.
Change tag name length limit in forms from 64 to 128 to match model.
Change naming of form field in admin/tags/edit action (minor, internal change)
Change "admin/tags/edit" --> "admin/tags/edit_name".  Also, make the view's
in_place_editi-ifying code a bit more specific.
Followon to "self" --> "static" change - revert accidental changes to Formo.
Use tag slugs to define tag URLs instead of ids.
- add slug to model, along with business logic.
- change tag URLs to use slugs in model and init (routing)
- change installer to add slugs to existing tags.
- change tag admin screen to show URLs.
- add edit form to admin screen to allow direct editing of URLs (and names).
- add comments to Controller_Items referring to tag edit form.
- @todo: add slug-related unit tests, add multi-tag routing, add tag album.
- @todo: move Item::convert_filename_to_slug() and Controller_Tag methods.
Consolidate a couple tag error message definitions.
Remove unneeded hidden form field in Controller_Tags::action_add().
Merge Controller_Tag into Controller_Tags.  There's no reason to separate these.
Refactor how Controller_Tags::action_show() interprets the route a bit.
Fix formatting in admin/tags view.
Revise how pagination in Controller_Tags::action_show() gets tag URL.
Remove Model_Tag::items(), similar to Model_Item::children() removal.
Remove Model_Tag::items_count(), similar to Model_Item::children_count() removal
Make tag RSS show all non-album items (instead of only photos).  Very old bug...
Update Formo to newest master branch (in sync with vendor).