better documenting multiple mouse click modifiers behaviour

[keszegh]

http://docs.giderosmobile.com/reference/gideros/Sprite/Event.MOUSE_DOWN#Event.MOUSE_DOWN
it works with adding them up (as they are powers of two) but this should be in the reference as e.g. if
shift AND ctrl is pressed then
modifiers~=KeyCode.MODIFIER_SHIFT
contrary to what the documentation suggests. so one actually needs to check the appropriate bit of the 'modifiers' value.

[mokalux]

I have added an example that show case mouse event modifiers:
https://wiki.giderosmobile.com/index.php/Event.MOUSE_DOWN

If that is enough we may close this issue.

[keszegh]

thanks, yet i don't think it makes clear that modifiers are additive.