Revert "Revert "jQuery.widget: Documenting 1.11's instance method for all widgets.""

This reverts commit cd2e4fbe6e282f9957e2e2b4f13996190e83f211.
Revert "Revert "jQuery.widget: Document that instance can be called on any element to determine whether it is a widget.  Fixes #77.""

This reverts commit 404a476727ed1b81ec791a53a107b712c9002317.
Manifest: Generate categories.json manifest

- Get categories metadata and extend it with its posts by using
  wordpress-walk-posts
Dialog: Remove array and string notations for position option.