Option to remove imported files

[jakubpawlowicz]

Opened by @mikkotikkanen in clean-css repo - moving it here as it'll be a CLI feature.

Note that API already exposes a list of imported files under inlinedStylesheets field in output hash.

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If you are running master css file which is just split with imports, it would be nice to have r.js styled removing of the imported files

Ie. if

master.css

@import('buttons.css')
body { background: #fff; }

buttons.css

.btn { background: #bada55; }

Would then become...

master.css

.btn { background: #bada55; }
body { background: #fff; }

...with buttons.css removed.

If file is not imported anywhere, it would be just minified as usual.