Allow transform callback to return a promise

[simonsmith]

As part of the async API it'd be great to return a promise from the transform method. The reason is to allow usage of postcss plugins that are async, like 3.x of stylelint.

transform(css, filename) {
  return processor.use(stylelint).process(css, {from: filename});
}

Unless there's a way to do something like this already?

[MoOx]

Don't think it's supported at the moment.
PR welcome.

[TrySound]

Seems like an interesting idea of integration.
/cc @davidtheclark @jeddy3

[TrySound]

@jeddy3 Only after dev merge which will be after I'll create this plugin. Give me a few days.

[simonsmith]

Awesome, thanks for adding this @TrySound

[MoOx]

So this is good now @TrySound?