More flexible close completion, blurry image fix and more

1. There is no way to set a completion block for tapping the area outside menu items. I add a property `closeCompletionHandler`, but may be confused with `-closeWithCompletion:`, I suggest make this method private.

2. fix blurry image (when its width is odd) in menu item view.

3. Let `REMenuItem` behaviors as UIControlEventTouchUpInside, give user the opportunity to cancel if tap wrong item accidentally.