Implement db#clear across the board

[vweevers]

Background: Level/abstract-leveldown#24 (comment).

Phase 1: get it working

• The default implementation of clear() deletes entries with an iterator. It can take range options, e.g. clear({ gt: 'foo' }) and should serialize them
  • PR: Add clear() abstract-leveldown#310
  • Release: 6.1.0
• encoding-down can call this.db.clear() and should encode the range options
  • PR: Support clear() encoding-down#89)
  • Release: 6.2.0
• leveldown
  • PR: Update abstract-leveldown to the latest version 🚀 leveldown#660
  • Release: 5.2.0
• deferred-leveldown should defer it
  • PR: Update abstract-leveldown to the latest version 🚀 deferred-leveldown#72
  • Release: 5.2.0
• levelup
  • PR: Add clear() levelup#669
  • Release: 4.2.0
• memdown
  • PR: Update abstract-leveldown to the latest version 🚀 memdown#194
  • Release: 5.0.0
• level-packager (bump dependencies to prevent dedupe)
  • Commit: Level/packager@a293d30
  • Release: 5.0.3
• level-js
  • PR: Support clear() level-js#182
  • Release: 5.0.0
• level
  • PR or commit: Document manifest, iterator() and clear() level#162, Level/level@5efdc82
  • Release: 6.0.0
• level-mem (bump dependencies to prevent dedupe)
  • Commit: Level/mem@baec173
  • Release: 5.0.1
• rocksdb
  • Commit: Level/rocksdb@b9d58fb
  • Release: 4.1.0
• level-rocksdb (bump dependencies to prevent dedupe)
• subleveldown uses the range options to implement clear on a sublevel
  • PR: Polish clear() subleveldown#74
  • Release: 4.1.2
• multileveldown (and by extension, level-party)
  • Level/multileveldown@47e0137
  • Release: 5.0.0
• leveldown-hyper and level-hyper (slated to be deprecated)

Phase 2: optimize

• memdown: Optimize db.clear() memdown#213
• leveldown can implement it natively (Optimize _clear() leveldown#680)
• rocksdb: Add db.getMany(keys) rocksdb#184 (5.2.0)
• level-js can call either IDBObjectStore#clear() or IDBObjectStore#delete(range)

On the side

• Use it in mafintosh/level-temp (old)
• Add notice to Raynos/level-delete-range (old)
• Recommend builtin db.clear() juliangruber/level-delete-stream#3
• Send PR to noffle/kappa-view-level for its clearIndex()

[ralphtheninja]

Very nice. I especially like the subleveldown feature, like emptying a bucket of stuff.

[vweevers]

Because abstract-leveldown@6.1.0 now has a clear() method, I'm moving this issue to community to track overall progress.