Add support for customizing publicPath

[pcardune]

Since image assets can take up quite a lot of bandwidth and storage space, it's nice to be able to have them served directly from a cloud storage service like S3.

In this PR I've added a new configuration option, imagesPublicPath, which allows you to customize the url generated by file-loader. For example, if you were using google cloud storage:

const optimizedImages = require('next-optimized-images');

let imagesPublicPath;
if (process.env.NODE_ENV === 'production') {
  imagesPublicPath = "https://storage.googleapis.com/my-bucket/images";
}

module.exports = optimizedImages({imagesPublicPath})({
  //...next config here
});

Then after building your application, you would sync the images to google cloud storage:

next build
gsutil -m rsync -r .next/dist/static/images gs:https://my-bucket/images

[codecov]

Codecov Report

Merging #9 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master     #9   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          42     42           
  Branches       13     13           
=====================================
  Hits           42     42

Impacted Files	Coverage Δ
index.js	100% <ø> (ø)	⬆️

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[cyrilwanner]

Cool, this is really useful 👍
Thank you very much for the contribution @pcardune :)

[cyrilwanner]

This improvement has been published to npm with version 1.2.2