add pathPrefix to bundle config

[chmontgomery]

Currently, you can define the pathPrefix for your url paths as an option to bundle.results. This applies to all bundles. Ideally, we should be able to be more granular by defining a pathPrefix option to each bundle individually, e.g.

// bundle.config.js
module.exports = {
  bundle: {
    main: {
      scripts: [
        './content/**/*.js'
      ],
      styles: [
        './content/**/*.css'
      ],
      options: {
        pathPrefix: { // {(string|object)}
          scripts: '//ecd.akamai.net',
          styles: '//a2b1.akamaihd.net'
        }
      }
    }
  }
}

[chmontgomery]

note: related to #22