Extended $elemMatch operators

Support all operators in where style, as well as `and` and `or`

```
$user = User::where('_id',1)
           ->elemMatch('mix', 'n', 3)
           ->orElemMatch('mix','n','>', 10)
           ->orElemMatch('mix','n','!=','x')
           ->first();
```
This will select the **first** element of `mix` subdocument where `n = 3 OR n > 10 OR n != x` applied to all `mix` subdocuments is true.

Not tested with multiple nesting levels.
Removed echo