Fix warnings reporting and stdlib warnings (#367)

* Fix stdlib warnings

* Mark unused includes when used from non-included files

* Do not mark indirectly included files as unused

* Show unused include warning only for files that are never used

* Remove unused include from Option.aes

* Consider functions passed as args as used

* Return warnings as a sorted list

* Fix failing tests

* Fix dialyzer warning

* Fix warning in Func.aes

priv/stdlib/Func.aes

@@ -2,7 +2,7 @@ namespace Func =
 
   function id(x : 'a) : 'a = x
 
-  function const(x : 'a) : 'b => 'a = (y) => x
+  function const(x : 'a) : 'b => 'a = (_) => x
 
   function flip(f : ('a, 'b) => 'c) : ('b, 'a) => 'c = (b, a) => f(a, b)