3.1 “Satyameva Jayate”
- Do not remove comments from prefixed values (by @rousso1).
- Allow Safari 6.1 to use final Flexbox spec (by @radium-v).
- Fix `filter` value in `transition` in Webkits.
- Show greetings if your browsers don’t require any prefixes.
- Add `<=` and `<` browsers requirement (by @papandreou).