Add action that enables custom rewrite rules to be added

[timrross]

This PR adds an action hook after the main page rewrite rules have been added, that allows setting up of extra rewrite rules based on the new rewrite slug that's defined in this plugin.

Use case 1:
I need to add an extra rewrite that allows the year to be appended to the end of the url to browse the 'portfolio' cpt archives by year.

function my_page_for_portfolio_rewrite_rules($archive_slug, $post_type, $args) {
    global $wp_rewrite;
    add_rewrite_rule( "{$archive_slug}/([0-9]{4})/?$", "index.php?post_type=$post_type" . 'year=$matches[1]' .  'top' );
    if ( $args->rewrite['pages'] ) {
        add_rewrite_rule( "{$archive_slug}/([0-9]{4})/{$wp_rewrite->pagination_base}/([0-9]{1,})/?$", "index.php?post_type=$post_type" . '&year=$matches[1]' . '&paged=$matches[2]', 'top' );
    }
}
add_action('page_for_portfolio_rewrite_rules', 'my_page_for_portfolio_rewrite_rules', 10, 3);

Thanks,
Tim

[roborourke]

Interesting use case. I had thought that date based archives should be automatically generated for non-hierarchical post types but if not it's something this plugin should add support for.

Happy to include this action hook anyway, just added a suggestion to apply then good to go.

[roborourke]

Need to match the existing code style here, it's also good to add doc blocks to actions and filters.

Suggested change

	do_action("page_for_{$post_type}_rewrite_rules", $archive_slug, $post_type, $args);
	/**
	* Action called after generating initial rewrite rules for a page as post type archive.
	*
	* @param string $archive_slug The slug for the post type archive page.
	* @param string $post_type The post type name.
	* @param WP_Post_Type $post_type_object The post type object.
	*/
	do_action( "page_for_{$post_type}_rewrite_rules", $archive_slug, $post_type, $args );