4.0!

Same as 4.0.0-alpha-1 - 09/06/17

• BREAKING: Remove overly-opinionated baseline type tools
  including font-size and baseline mixins.
  These settings are more clear when established explicitly in CSS
• BREAKING: Rename scale() => ratio() to avoid conflicts with CSS
• BREAKING: Remove stand-alone browser-ems() function…
• NEW: Allow browser-ems as a $to-unit argument
  in the contert-units() function.
• NEW: Add (private) pow() functions,
  so that MathSass is no longer a dependency for non-integer steps