Secrets API search added. Removed older functions. Backwards compatibility.

Secrets API search added.  Removed older functions.  Backwards compatibility.

* auth-source.el (auth-sources): Allow for simpler defaults for Secrets
API with a string "secrets:collection-name" and with 'default.
(auth-source-backend-parse): Parse "secrets:collection-name" and
'default.  Recurse on parses instead of repeating code.  Use the
Secrets API is the source is not nil and 'ignore otherwise.  Emit a
message when ignoring a source.
(auth-source-search): List ignored search keys at the top level.
(auth-source-netrc-create): Use `case' instead of `cond'.
(auth-source-secrets-search): Created with TODOs.
(auth-source-secrets-create): Created with TODOs.
(auth-source-retrieve, auth-source-create, auth-source-delete)
(auth-source-protocol-defaults, auth-source-user-or-password-imap)
(auth-source-user-or-password-pop3, auth-source-user-or-password-ssh)
(auth-source-user-or-password-sftp)
(auth-source-user-or-password-smtp): Removed.
(auth-source-user-or-password): Deprecated and modified to be a wrapper
around `auth-source-search'.  Not tested thoroughly.