v2.1.0

Changed

• Use standard for linting (@mafintosh)
• Upgrade abstract-leveldown from ^2.1.0 to ^2.4.1 (@mafintosh)
• Upgrade levelup from ^0.19.0 to ^1.2.1 (@mafintosh)
• Upgrade memdown devDependency from ^1.0.0 to ^1.1.1 (@mafintosh)
• Upgrade tape devDependency from ^3.0.3 to ^4.2.2 (@mafintosh)
• Add opts parameter to SubDown for custom open logic (@mafintosh)
• Add opts.open open hook (@mafintosh)