Internally shim Object.create

[briancavalier]

See #16. Currently, meld will account for a missing Object.defineProperty, but relies on the environment (or polyfill) to provide Object.create. Seems like we should either account for both, or account for neither and force people to use a polyfill.

I wouldn't want to go shimming much more than those two, so it's a bit of a slippery slope, but two seems ok.