Automatically bind store methods

[rymohr]

Bind store methods for consistent behavior with react components.

@spoike react requires an es5 shim if you want to support older browsers so I'm not sure there's a need to include a Function.prototype.bind polyfill:

http://facebook.github.io/react/docs/working-with-the-browser.html#browser-support-and-polyfills
https://github.com/facebook/react/blob/2bdad81955e160a5b11110b40c7222a1113cc1fb/src/browser/ui/React.js#L150

[krawaller]

Since Reflux is pretty useful without React I think it should be able to stand on its own legs regarding the shims, and not rely on React's es5 stuff.

[rymohr]

I was curious if anyone was using it without react. I think facebook's policy of not including es5 shims is a good one in general, but it would be good to raise a warning and add a note to the readme in that case.