[data-flout] and purgecss

[renatodeleao]

We (will) recommend using purgecss (or other dead css remover) to strip down the great ammount of responsive classes that are not used.

Current attribute selectors are always left in the bundle.

• https://github.com/FullHuman/purgecss/issues?utf8=%E2%9C%93&q=attribute+selector

This is not an issue per se, but it's worth mentioning to keep and eye on the package for an expected fix for version 2.

[renatodeleao]

Investigate moving to https://github.com/leeoniya/dropcss, which supports attribute selectors