Does not capture, handle or pass-on error states

[rvagg]

LevelUP, AbstractLevelDOWN and LevelDOWN do a lot of argument sanity checking to make sure you get a sensible error in the right way if you do something wrong. Sublevel now doesn't pass everything on early enough to return the correct error types.

I have this in an the tests for level-ttl which is failing:

  t.throws(db.put.bind(db), { name: 'WriteError', message: 'put() requires key and value arguments' })
  t.throws(db.del.bind(db), { name: 'WriteError', message: 'del() requires a key argument' })

I now get an uncaughtException for this because it bubbles up through EventEmitter rather than being thrown straight from the callsite:

Error: value cannot be `null` or `undefined`
    at Object.apply (/home/rvagg/git/level-sublevel/nut.js:73:23)

Basically, sublevel is now returning faux-levelup that doesn't behave the same as levelup. I don't really have a suggestion for the best way forward except that perhaps we need ab AbstractLevelUP just for this!