Update count.md

* Some formatting
* Some aligning
* Removed extra arg in method header

### Additional
Do we really want to make `criteria` a required parameter? What if you want to know how many records there are in total? We could just say:

```javascript
if (typeof criteria === 'function') {
  callback = criteria;
  criteria = {};
}
```
Update count.md

Alignment and spacing
Updated args
Merge pull request #193 from RWOverdijk/patch-1

Update count.md