Summary: I am unsure whether there was a reason not to use an `index.js` file from the beginning. It always struck me as confusing and odd to have the main API hidden in a folder somewhere. This changes RN to use the standard `index.js` file that is common in almost all JavaScript packages.
Reviewed By: yungsters, rubennorte
Differential Revision: D17314423
fbshipit-source-id: 10eaf4fddd41e91163de7d10c0879b623dab00d7
Christoph Nakazawa