Fix some documentation errors.
Fix some documentation errors.

Properly define and document the wrapper function (as required in the proptypes).

"preloader" prop only accepts a function, not a React component (as required in proptypes).

ta2edchimp/react-imageloader,beni55/react-imageloader,ta2edchimp/react-imageloader,beni55/react-imageloader,hzdg/react-imageloader,hzdg/react-imageloader