Update to Webpack 2

[ephys]

Related issue: https://github.com/timse/srcset-loader/issues/6

List of changes:

• Updated (dev)Dependencies.
• Updated the examples and the readme to use the webpack 2 prefered configuration format.
• Added Unit Tests.
• Source code is now full es6+ and is transpiled to es5.
• placeholder can now be used even if sizes is not specified. The original image will be returned along with the placeholder.
• placeholder now accepts the width of the placeholder as a parameter.
• sizes now accepts "default" as a possible value, which adds the original image to the list of sources.
• Added a check to prevents using the pixel density descriptor format \d+x (ex: 2x) as a size, which before now would have returned a picture with a width of 2px.
• Added a new lightweight option, which disables generating the data that can be computed at runtime:
  • out.srcSet is removed from the output as it can be computed using out.sources
  • out.placeholder does not return an SVG anymore, only the raw image in base64.
  • Utilities are available in srcset-loader/runtime to generate both the srcSet string and the svg.
• placeholder.color now returns the alpha channel as a float instead of an int.

[timse]

awesome! 🎉 Thanks so much :)! Will merge this before it gets old, if you dont mind, there might be some stuff that could be unified to reduce duplication?

Cheers!

[ephys]

Of course, feel free to point out which parts you'd like to see unified :)