Show larger images on fullscreen

Is there any way to pass a separate set of images for fullscreen mode?

It makes sense to request small images originally, and then request large images if/when fullscreen is enabled. This can help save a lot of bandwidth. Something like:

const images = [
      {
        original: 'http://lorempixel.com/1000/600/nature/1/',
        thumbnail: 'http://lorempixel.com/250/150/nature/1/',
        fullscreen: 'http://lorempixel.com/2000/1200/nature/1/',
      },
      {
        original: 'http://lorempixel.com/1000/600/nature/2/',
        thumbnail: 'http://lorempixel.com/250/150/nature/2/'
        fullscreen: 'http://lorempixel.com/2000/1200/nature/2/',
      },
      {
        original: 'http://lorempixel.com/1000/600/nature/3/',
        thumbnail: 'http://lorempixel.com/250/150/nature/3/'
        fullscreen: 'http://lorempixel.com/2000/1200/nature/3/',
      }
    ]

[xiaolin]

I do plan to rewrite most of the lib and document it better.

I will try to get to this soon if no one opens a PR.

[xiaolin]

see #395. Feel free to open a pr if you like, otherwise, I will try to get this done on the next release.