Change the type of cookie name to binary()

The API will be more consistent like this, and we can ensure
that duplicate cookie names are never sent.

doc/src/manual/cowboy_req.set_resp_cookie.asciidoc

@@ -14,13 +14,11 @@ set_resp_cookie(Name, Value, Req :: cowboy_req:req())
 set_resp_cookie(Name, Value, Opts, Req :: cowboy_req:req())
     -> Req
 
-Name  :: iodata()                  %% case sensitive
+Name  :: binary()                  %% case sensitive
 Value :: iodata()                  %% case sensitive
 Opts  :: cow_cookie:cookie_opts()
 ----
 
-// @todo I am not particularly happy about the fact that the name is iodata().
-
 Set a cookie to be sent with the response.
 
 Note that cookie names are case sensitive.
@@ -53,6 +51,7 @@ otherwise the cookie will not be sent in the response.
 == Changelog
 
 * *2.0*: `set_resp_cookie/3` introduced as an alias to `set_resp_cookie/4` with no options.
+* *2.0*: The first argument type is now `binary()` instead of `iodata()`.
 * *1.0*: Function introduced.
 
 == Examples

src/cowboy_req.erl

@@ -556,7 +556,7 @@ set_resp_cookie(Name, Value, Req) ->
 %% The cookie value cannot contain any of the following characters:
 %%   ,; \t\r\n\013\014
 %% @todo Fix the cookie_opts() type.
--spec set_resp_cookie(iodata(), iodata(), cookie_opts(), Req)
+-spec set_resp_cookie(binary(), iodata(), cookie_opts(), Req)
 	-> Req when Req::req().
 set_resp_cookie(Name, Value, Opts, Req) ->
 	Cookie = cow_cookie:setcookie(Name, Value, maps:to_list(Opts)),