Connector Ref Updates

[darthtrevino]

• Documentation updates
• Update the connector ref mechanism so we provide a function that creates refs instead of creating refs aggressively. This will also allow us to pass options into the connector-ref functions
• Update: I did not like how the new API was evolving, so I've pared this back to just allowing the connect function to accept a ref object.

function Box({dragSource}) {
  return <div ref={dragSource}>...</div>
}
export default DragSource(ItemTypes.Box, {/*...*/}, (connect, monitor) => ({
  dragSource: connect.dragSourceRef()
}));