Implemented ?offset= parameter and added meta.total entry to results. 

Hello,

Sorry for long reply, we haven't visited this repository for a while. Here's a little piece of feedback. 

* `adapter.count` doesn't apply `req.query.filter` which doesn't seem to be correct.
* `adapter.count` appears to run sequentially. Which is not really critical but a bit suboptimal. It would be much better to run  `adapter.count` in parallel with `adapter.find`.
* It makes sense to make `count` optional with `req.query.includeMeta` or something alike.