@spec no_duplicate_slugs([Postex.Post.t()]) :: [Postex.Post.t()]

Raises if there are any duplicate slugs

@spec prefix_defined(binary() | nil) :: :ok

Raises unless the prefix is set for the use Macro, i.e.

use Postex, prefix: "https://www.yoursite.com/posts/"

or is explicitly disabled, i.e.

use Postex, prefix: false

@spec url_length([Postex.Post.t()], false | binary()) :: [Postex.Post.t()]

Raises unless all urls (prefix + slug) are less than 60 characters (for SEO) as per Neil Patel.

Feature can be disabled by setting prefix to false