Improve browser bundling with Browserify/Webpack

This preps this package for `v1.0.1`, by updating the `intl-*` dependencies, and refactors this package to be more inline with how react-intl is structured.

The `"browser"` field has been added to the `package.json` to ignore all the locale data, expect English, when bundling with Browserify or Webpack.

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~~**Note:** The build will likely fail because of https://github.com/benjamn/recast/issues/135~~