PHP 7.0 onwards support return type declarations which I feel we should encourage in new APIs.

We need to confirm the coding style of these.

Examples:

    public static function get_reason() : string {

    }

    public static function get_reason(): string {

    }

    public static function get_reason():string {

    }

    public static function get_reason() :string {

    }

My personal preference is for the first example, which has one space before, and one space after the colon.