Chained batches not supported in 6

[TehShrike]

I'd hacked chained batches into sublevel 5, but it looks like they're not supported in 6 at the moment.

[dominictarr]

I only left them out because I pretty much never use them.
that is correct - I will merge if you make a PR.

It would be best if we could hook into levelup/lib/batch to do this... even if we have to make a pull request there. That would make levelup more modular.

[kessler]

Is this: https://github.com/dominictarr/level-sublevel/blob/master/batch.js a work in progress? (since I only see put and del there)