Add `has()` and `hasMany()`

[vweevers]

Per the feature request of #106. Will add two methods:

await db.put('love', 'u')
await db.has('love') // true
await db.hasMany(['love', 'hate']) // [true, false]

Tasks:

• level-supports (6.2.0): Add has property supports#33
• abstract-level (3.0.0): Implement has() and hasMany() abstract-level#96
• memory-level (3.0.0): Implement has() and hasMany() memory-level#18
• classic-level (3.0.0): Implement has() and hasMany() classic-level#111
• browser-level (3.0.0): Implement has() and hasMany() browser-level#25
• level (10.0.0): bump dependencies
• many-level: implement has() and hasMany()
• rave-level: implement has() and hasMany()