Replace precss with individual plugins about vuepack

[egoist]

I'd like to replace them with some better alternatives, do you have any suggestions about what should be included? PRs are welcome too 🙂

[dodas]

Starting with precss,

I removed:

postcss-custom-properties - already have Sass-like postcss-advanced-variables, and cascading feature of custom properties cannot be mimicked / transformed to CSS3.
postcss-nested - already have Sass-like postcss-nested which does not require & everywhere.
postcss-atroot - I don't see usefulness with Vue component, as everything should be under component's namespace. But maybe someone would find it useful.
postcss-custom-selectors - I just don't use it.

And I added:

postcss-nested-ancestors - I use it to reference parent selector combined with state selector. Example:

.entry {
  ...

  &-info {
    display: none;

    ^&.is-selected & {
      display: block;
    }
  }
}

outputs:

.entry {
  ...
}

.entry-info {
   display: none;
}

.entry.is-selected .entry-info {
  display: block;
}

I think it's nice.. :)

And this is the order which I require plugins in:

require('postcss-nested-ancestors'),
require('postcss-partial-import'),
require('postcss-mixins'),
require('postcss-advanced-variables'),
require('postcss-custom-media'),
require('postcss-media-minmax'),
require('postcss-color-function'),
require('postcss-extend'),
require('postcss-nested'),
require('postcss-property-lookup'),
require('postcss-selector-matches'),
require('postcss-selector-not'),

Should I make a PR?

[egoist]

I just realized I did't use any postcss plugin specified syntax in the CSS, maybe we can simply remove precss and let user choose what plugins they want.

[dodas]

Yup, that would probably be nicest way.