v0.4.0

• Adds effectsAllowed: Array<DropEffects>? to beginDrag options and getDropEffect(effectsAllowed) to drop target so they can show different cursor depending on modes supported by drag source and drop target
• endDrag now accepts a recordedDropEffect: DropEffect instead of a boolean as an argument, falsy-checking code will work like before
• Adds a third parameter recordedDropEffect to endDrag that makes it possible to find out if some nested drop zone already handled drop
• Makes browser's "+" icon next to dragged item opt-in rather than opt-out