Members [is_user_logged_out] shortcode

Skildring

To complement the [is_user_logged_in] shortcode I noticed a [is_user_logged_out] shortcode was missing from Members plugin, soI decided to write an «extension plugin» to add it. Maybe this can be added to Members itself one day?

The [is_user_logged_out] shortcode should be used to check if a user is currently logged out of the site. If not, the content will be hidden.

Example:
[is_user_logged_out]This content is only shown to logged-out users.[/is_user_logged_out]

This shortcode has no parameters.