Concatenate non-jQuery dependencies with Webpack

Run `webpack -p` to prepare for production (check in bundle.js).
Run `webpack --watch --colors` to watch and run in development.

* All files are written to public/js/dist/bundle.js, which is included
  in the HTML in a `<script>` tag
* expose/exports/script shim loaders included to impose smallest changes
  possible on MIDI and other required libraries
* index.js exposes `songOfGitHub` to the global context to impose
  smallest changes necessary to start using Webpack.
Remove unused vars and arguments found by Webpack
Enable GZIP compression for responses from Express

This includes HTML and static asset compression since Express is serving
the public endpoint as well. This gives a ~60% size savings for
bundle.js.
Use song-of-github as name instead of placeholder
Add run & development info to README
Add `build` and `watch` commands for easier dev
Compress JS for distribution
Merge pull request #30 from ssorallen/webpackify

Webpackify