Adding elementRef for parent component.

[dfbaskin]

Added elementRef property for passing generated element to parent property. Also added component rendering tests.

[dfbaskin]

An example of why the elementRef is needed (in order to measure the div element).
https://github.com/dfbaskin/react-mouse-touch-events

[MilllerTime]

This is a useful feature, thanks @dfbaskin! Definitely appreciate the render tests, too.

For your information, I merged this from the command line after fetching your commits and creating a new local branch, then rebasing with some code style tweaks. Looks like GitHub didn't exactly pick up on that, so I'm manually closing this since your commits are applied to master.

[dfbaskin]

Thanks!