a_z_shortcode_handler( array $attributes )

function a_z_shortcode_handler( $attributes ) {
	$attributes = shortcode_atts( array(
		'column-count' => 1,
		'minimum-per-column' => 10,
		'heading-level' => 2,
		'post-type' => 'page',
	), $attributes, 'a-z-listing' );

	$post_types = explode( ',', $attributes['post-type'] );
	$post_types = array_unique( $post_types );
	$post_types = array_map( function( $item ) {
		return trim( $item );
	}, $post_types );

	$query = array(
		'post_type' => $post_types
	);
	$a_z_query = new A_Z_Listing( $query );
	return $a_z_query->get_the_listing();
}