v5.0.0-alpha.1

V5: faster, more detailed and browser compatible

• Drop support for Node 8 and 10 (Node.js releases)
• Rename all metrics ending on .share to .ratio
• Rename stylesheets to stylesheet
• Remove stylesheets.browserhacks
• Remove stylesheets.cohesion (now rules.selectors.mean)
• Remove atrules.documents
• Remove atrules.mediaqueries.browserhacks
• Add atrules.keyframes.prefixed
• Drop atrules.namespace.*
• Drop atrules.page.*
• Drop atrules.supports.browserhacks.*
• Remove stylesheets.simplicity(now rules.selectors.mean)
• Add rules.selectors.mean/median/mode/etc
• Add rules.declarations.mea/median/mode
• Remove selectors.js.*
• Add selectors.specificity.*
• Add selectors.complexity.*
• Remove selectors.browserhacks.*
• Remove values.total
• Remove values.browserhacks.*
• Remove values.colors.duplicate.*

Closes #207, #206, #200, #184, #183, #181, #148, #142, #129, #121, #83, #59