[timer] Rework new() consistently with other classes.

timer.lua

@@ -194,8 +194,11 @@ __index = function(tweens, key)
 end})
 
 -- Timer instancing
-function Timer.new()
-    return setmetatable({functions = {}, tween = Timer.tween}, Timer)
+function Timer:new(args)
+    self = setmetatable(args or {}, self)
+    self.functions = {}
+
+    return self
 end
 
 return Timer