Performance rewrite

This rewrite helps make styled-system smaller, faster, and simplifies the API.

Added

• variant
• compose
• mixed

Changed

• style utility is now responsive by default
• All built-in style functions now support responsive array values
• backgroundImage no longer wraps values with url()
• buttonStyle prop has been renamed to variant
• The style utility getter argument has beend renamed to transformValue
• util.get no longer supports a fallback argument

Removed

• responsiveStyle use style instead
• complexStyle use variant instead
• complexStyle (variant) boolean props are no longer supported
• pseudoStyle
• hover
• focus
• active
• disabled
• fontSize and width no longer support shorthand props
• alias option
• numberToPx option (pass util.px to the transformValue argument instead)
• util.media
• util.neg
• util.arr
• util.getWidth
• util.mq
• util.fallbackTheme
• util.breaks
• util.dec
• util.getValue

Migrating from v2

• Replace all deprecated shorthand f props with the fontSize prop
• Replace all deprecated shorthand w props with the width prop
• Replace the deprecated buttonStyle prop with the variant prop
• Ensure backgroundImage props include the CSS url() syntax where needed
• Replace instances of responsiveStyle with the style utility
• Replace the numberToPx argument with transformValue: util.px
• Rename the getter argument with transformValue
• Replace complexStyle with variant
• Replace custom alias props with something like recompose's mapProps
• Ensure boolean props are not used for variant styles, including:
  • buttonStyle
  • textStyle
  • colors
• If you were using hover, focus, active, disabled, or pseudoStyle, consider adding your own replacement
• Consider adding replacements for any of the removed utilities listed above