Finish adding Rollup / npm package

[alexlenail]

Although the javascripts / css are now on UNPKG, I haven't finished adding Rollup to create minified scripts, or nice module definitions. I don't know how javascript modules should look for Axial, but here are some pointers to my future self or someone else.

• http://exploringjs.com/es6/ch_modules.html
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import
• https://github.com/d3/d3/blob/master/package.json
• https://rollupjs.org/guide/en
• https://github.com/rollup/rollup-starter-lib