Improve browser bundling with Browserify/Webpack

This adds a `"browser"` field to the `package.json` file to hint to
both Browserify and Webpack that they should _not_ include the data for
all locales (just English) when bundling for the browser.
Merge branch 'master' into browserify
Merge pull request #87 from ericf/browserify

Improve browser bundling with Browserify/Webpack