Sourcemaps optional

[Wolfr]

We could provide an option if you want to see sourcemaps from the CSS or not.

css: {
  sourcemaps: false
}

There should probably be a split between Bedrock sourcemaps and production sourcemaps, and the implementation is probably different between sass.js and postcss.js.

Personally I am never bothered by sourcemaps being in the build files, even for production websites, but maybe there are other opinions out there.