Added ComponentScope.stateIO
SyntheticEvent now covariant
SyntheticEvent.dragEvent added
Added {preventDefault,stopPropagation}{F,IO}
Added component state modStateIOM, tweaked runStateIO*
Added ComponentStateFocus
Revised how optional callbacks are handled
modState() now only stores the new state if it's changed.
HTML5 attributes for drag-and-drop.
Added modState{O,U}