Upgrade to React 0.12.0.

Fixes #28.

Squashed commit of the following:

commit f64f7daba3e63d2305100bb112f5490646da19ad
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 12:15:54 2014 +1100

    HISTORY.md: 0.6.0 notes

commit e140fa09956f1667cb4af009eed0e7bc104ef1c4
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 12:03:38 2014 +1100

    Edges

commit d1fc1994051b2152f4775a1c2881aa4a0f10451d
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 11:12:37 2014 +1100

    Restore and deprecate VDom

commit b98724be476009580595d894987cebea0bfff075
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 10:23:17 2014 +1100

    Updated React top-level API to React 0.12

commit 3d1cb766d110e00e418989d6515ae2216fbb05dd
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 09:55:17 2014 +1100

    Another rendering test

commit 5ef08cfd4d28c4629069700b181e5bf41ffbb24b
Author: David Barri <japgolly@gmail.com>
Date:   Sun Nov 23 09:47:42 2014 +1100

    React.createElement docs lied. Fixed. All tests now pass.

commit 250ea38d9660b350c580a4582a2eaebd97eb5a52
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 22:55:21 2014 +1100

    Got the little bastard!

commit 7305be07a72e2cfbb37687c6a5c68ce4afed965e
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 21:19:14 2014 +1100

    ReactNode rendering

commit 63597869b8366868e57e597449310eaa82311f3c
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 20:21:27 2014 +1100

    ReactElement and ReactNode now rule the day. Tests rebel.

commit 357fb794589915ecef83d93ca5831ec130a993be
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 19:44:38 2014 +1100

    Tests pass again

    Moved key off props.
    Created ReactElement{,_} although not doing much with it yet.

commit 3242b995bdcec4d21e12cd1b3001aee83358de3f
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 19:42:41 2014 +1100

    createFactory ∘ createClass

commit 52ba75fe1fe7f1f42baa3d96e8ff91f3da5cccd3
Author: David Barri <japgolly@gmail.com>
Date:   Sat Nov 22 17:38:30 2014 +1100

    Upgrade React to 0.12.0