Return object _id after insertion

Hi Markus Siemens,

TinyDB is a great project and I've been enjoying using it.

I think return the object after insertion would be a good idea, after that I can get the id of the object been inserted.

Best Regards

Dinever
The iterable is consumed here, you *may* get an empty generator back. If you were going to return the ``eid`` when inserting the element you can just do:

```python
def insert_multiple(self, elements):
    return [self.insert(x) for x in elements]
```

Then you get a list of ``eid``s after inserting in bulk.