Add NPM Exports

[palmerj3]

I would like for you to create a file index.js in the root of the project that contains the proper module.exports for all of the major classes for shaka-player.

Currently the NPM dependency requires google closure compiler in order to be used and the individual namespaced classes are only available after including the script in head or .

Exposing module.exports would allow this lib to be used in a CommonJS environment more easily.

[palmerj3]

I've created a PR for this feature - please review when you have the chance. Thanks!

#35

[joeyparrish]

Closing now that #35 is merged. Thanks!