v6.0.0

If you are upgrading: please see UPGRADING.md.

Changed

• Breaking: bump abstract-leveldown (720aced) (Vincent Weevers)
• Breaking: bump buffer from 5.x to 6.x (#210) (cc68b21) (Alex Potsides)
• Modernize syntax and bump standard (Level/community#98) (0ce815f) (Vincent Weevers)
• Every browser in our test matrix now supports binary keys (2c20127) (Vincent Weevers)