enable sourcemap output other than inline about postcss-cssnext

[MoOx]

I don't use sourcemap (don't feel the need to), so feel free to take care of that.
PRs are always welcome :)

[lionelB]

Have in mind that the output of the postcss will change, and so the api of cssnext
(don't know how to deal with wemver anymay :D )

[MoOx]

It's not a problem. Don't think about semver now. We are below 1.0, so we can add breaking changes. And after 1.0, breaking changes will just bump to a major version.
We can (like you said) return the object if sourcemap is not inlined.

[lionelB]

okidoki i'll take it ;)

[Subash]

Any update on this ? I a trying to include this inside Prepros.

[lionelB]

thx!

[MoOx]

@Subash change released as 0.4.0
Tell me if you need anything ;)

[Subash]

@MoOx Thanks, added to Prepros 5.