v4.0.0

Added

• Import and fix gc test from levelup (@vweevers)
• Add standard (@ralphtheninja)
• Add a note on upgrading to 2.0.1/3.0.1 (@ralphtheninja)

Changed

• Upgrade to verify-travis-appveyor@^3.0.0 (@ralphtheninja)
• Change deprecated node-uuid to uuid (@ralphtheninja)
• Update README format (@ralphtheninja)

Fixed

• Fix docs for approximateSize() (@ralphtheninja)

Removed

• Remove node 4 from Travis and AppVeyor (@ralphtheninja)
• Remove TypeScript typings (@MeirionHughes)