Add onAuxClick to MouseEvents (#26)

Add onAuxClick for handling non-primary clicks such as middle click and
ctrl+click.
purescript-web/purescript-web-uievents#18

Co-authored-by: Joe Opseth <joe.opseth@outlook.com>

Author: joe-op

src/DOM/HTML/Indexed.purs

@@ -52,6 +52,7 @@ type GlobalEvents r =
 type MouseEvents r =
   ( onDoubleClick :: MouseEvent
   , onClick :: MouseEvent
+  , onAuxClick :: MouseEvent
   , onMouseDown :: MouseEvent
   , onMouseEnter :: MouseEvent
   , onMouseLeave :: MouseEvent