* auth-source.el (top): Autoload `secrets-list-collections',

* auth-source.el (top): Autoload `secrets-list-collections',
`secrets-create-item', `secrets-delete-item'.
(auth-sources): Fix tag string.
(auth-get-source, auth-source-retrieve, auth-source-create)
(auth-source-delete): New defuns.
(auth-source-pick): Rewrite in order to avoid 2 passes.
(auth-source-forget-user-or-password): New parameter USERNAME.
(auth-source-user-or-password): New parameters CREATE-MISSING and
DELETE-EXISTING.  Retrieve password interactively, if needed.