title: PostCSS plugin order when using with webpack
body: <p>I want to use the following postCSS plugins:</p>
  
  <ol>
  <li>postcssimport (<a href="https://github.com/postcss/postcss-import" rel="nofollow">https://github.com/postcss/postcss-import</a>)</li>
  <li>postcssnested (<a href="https://github.com/postcss/postcss-nested" rel="nofollow">https://github.com/postcss/postcss-nested</a>)</li>
  <li>postcsssimplevars (<a href="https://github.com/postcss/postcss-simple-vars" rel="nofollow">https://github.com/postcss/postcss-simple-vars</a>)</li>
  <li>postcssmixins (<a href="https://github.com/postcss/postcss-mixins" rel="nofollow">https://github.com/postcss/postcss-mixins</a>)</li>
  <li>autoprefixer (<a href="https://github.com/postcss/autoprefixer" rel="nofollow">https://github.com/postcss/autoprefixer</a>)</li>
  <li>lost (<a href="https://github.com/peterramsing/lost" rel="nofollow">https://github.com/peterramsing/lost</a>)</li>
  <li>postcssflexibility (<a href="https://github.com/7rulnik/postcss-flexibility" rel="nofollow">https://github.com/7rulnik/postcss-flexibility</a>)</li>
  </ol>
  
  <p>But I'm unsure of the order in which I should put them inside</p>
  
  <pre><code>postcss: function () {
    return [postcssimport, postcssnested, ...];
  }
  </code></pre>
  
  <p>Any help?</p>