Export getCroppedImg from package.

[cagosto]

What do you think about exposing the getCroppedImg function. So others can import from react-easy-crop?

[ValentinH]

I don't really want to have it part of the library because this function is tricky and is often a source of issues on some browsers like Safari mobile. Therefore, I prefer only providing it as example to avoid having to actually maintain it and provide support for it.