Add the remaining missing specs

Found thanks to warn_missing_spec and added with the help of typer.
Eunit functions do not have specs yet however.

rebar.config

@@ -1,6 +1,7 @@
 {cover_enabled, true}.
 {erl_opts, [
 %%	bin_opt_info,
+%%	warn_missing_spec,
 	warnings_as_errors,
 	warn_export_all
 ]}.

src/cowboy_clock.erl

@@ -60,6 +60,7 @@ rfc1123() ->
 
 %% gen_server.
 
+-spec init([]) -> {ok, #state{}}.
 init([]) ->
 	?TABLE = ets:new(?TABLE, [set, protected,
 		named_table, {read_concurrency, true}]),
@@ -69,28 +70,32 @@ init([]) ->
 	ets:insert(?TABLE, {rfc1123, B}),
 	{ok, #state{universaltime=T, rfc1123=B, tref=TRef}}.
 
+-spec handle_call(_, _, State)
+	-> {reply, ignored, State} | {stop, normal, stopped, State}.
 handle_call(stop, _From, State=#state{tref=TRef}) ->
 	{ok, cancel} = timer:cancel(TRef),
 	{stop, normal, stopped, State};
-
 handle_call(_Request, _From, State) ->
 	{reply, ignored, State}.
 
+-spec handle_cast(_, State) -> {noreply, State}.
 handle_cast(_Msg, State) ->
 	{noreply, State}.
 
+-spec handle_info(_, State) -> {noreply, State}.
 handle_info(update, #state{universaltime=Prev, rfc1123=B1, tref=TRef}) ->
 	T = erlang:universaltime(),
 	B2 = update_rfc1123(B1, Prev, T),
 	ets:insert(?TABLE, {rfc1123, B2}),
 	{noreply, #state{universaltime=T, rfc1123=B2, tref=TRef}};
-
 handle_info(_Info, State) ->
 	{noreply, State}.
 
+-spec terminate(_, _) -> ok.
 terminate(_Reason, _State) ->
 	ok.
 
+-spec code_change(_, State, _) -> {ok, State}.
 code_change(_OldVsn, State, _Extra) ->
 	{ok, State}.
 

src/cowboy_http_handler.erl

@@ -15,6 +15,8 @@
 -module(cowboy_http_handler).
 -export([behaviour_info/1]).
 
+-spec behaviour_info(_)
+	-> undefined | [{handle, 2} | {init, 3} | {terminate, 2}, ...].
 behaviour_info(callbacks) ->
 	[{init, 3}, {handle, 2}, {terminate, 2}];
 behaviour_info(_Other) ->

src/cowboy_http_websocket_handler.erl

@@ -15,6 +15,8 @@
 -module(cowboy_http_websocket_handler).
 -export([behaviour_info/1]).
 
+-spec behaviour_info(_) -> undefined | [{websocket_handle, 3}
+	| {websocket_init, 3} | {websocket_terminate, 3}, ...].
 behaviour_info(callbacks) ->
 	[{websocket_init, 3}, {websocket_handle, 3}, {websocket_terminate, 3}];
 behaviour_info(_Other) ->