The new set_cookie/3 function implements more complete RFC2109
cookie formatting than setcookie/6 and is 10x - 15x more efficient
than its old setcookie counterpart because of avoiding the use of
io_lib:format/2. The setcookie/2 through setcookie/6 are marked
as deprecated. The function is named set_cookie rather than setcookie
to facilitate the ease of depricating the old implementation.