v4.0.0

Changed

• Upgrade level-js from ~2.2.4 to ~3.0.0 (@vweevers, @Greenkeeper)
• Upgrade level-packager from ~2.1.1 to ~4.0.0 (@vweevers, @Greenkeeper)
• Upgrade memdown from ~2.0.0 to ~3.0.0 (@vweevers, @Greenkeeper)
• Upgrade leveldown optionalDependency from ~3.0.1 to ~4.0.0 (@vweevers, @Greenkeeper)
• Upgrade airtap devDependency from 0.0.4 to 0.0.8 (@vweevers, @Greenkeeper)
• Tweak copyright years for less maintenance (@ralphtheninja)
• Update repository url (@vweevers)

Added

• Add CHANGELOG.md (@ralphtheninja)
• Add UPGRADING.md (@ralphtheninja)