Output ES2015 module format

[nathanosdev]

Outputting ES2015 format would allow for projects importing this library to perform tree-shaking, removing any modules/components that they're not actually using.

At the moment, this isn't possible with Webpack but webpack/webpack#2933 is tracking the progress of its implementation.

It seems to be moving slowly, so depending on whether or not it actually gains traction, this project might need to move to another build system.

If it is implemented, the project should output 2 Webpack builds in parallel.

module.exports = [
  Merge(CommonConfig, {
    output: {
      filename: '[name].umd.js',
      libraryTarget: 'umd'
    }
  }),
  Merge(CommonConfig, {
     output: {
       filename: '[name].module.js',
       libraryTarget: 'es2015'
     }
   })
];