Replace ReactRender with IsReactElement

[natefaubion]

Fixes #131 #127

[ethul]

Looks great! Thanks for this update.

Just out of curiosity, should fragment be exported as well as fragmentWithKey?

[natefaubion]

I did not export fragment because that's what toElement [ ... ] is. I don't think there is a reason to expose the ReactClass directly.

[ethul]

Gotcha. Sounds good. Thanks again.

[paulyoung]

Perhaps this would help with discoverability.

fragment :: Array ReactElement -> ReactElement
fragment = toElement

Not being able to find fragment led to someone using fragmentWithKey instead, and I eventually found this thread.

[ethul]

I can see this being handy to match up with React.Fragment in JS. However, I am open to opinions on this. If we all think this would be helpful, @paulyoung can you please open a new issue for this? Thanks!