Added orient="ndarray" to DataFrame.to_dict()
It would be useful to allow Series to be directly converted to numpy arrays instead of having to do this outside.

Hello @LarsKue! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-03-08 20:48:26 UTC is this really that useful, its only a one-line transformation?

```
df = pd.DataFrame({'a': [1,2], 'b': [3,4]})
dict_arr = {k: np.array(v) for k, v in df.to_dict(orient='list').items()}
``` > is this really that useful, its only a one-line transformation?

If you consider this not useful, the entire `to_dict` method should also be considered not useful, since it does exactly this for other types.

Edit: Analogous outside code is
```
df = pd.DataFrame({'a': [1,2], 'b': [3,4]})
dict_arr = {k: v.to_numpy() for k, v in df.items()}
```

To me it seems natural `to_dict` should be able to convert to `np.ndarray` since `pandas` otherwise has great integration for `numpy` arrays, etc. `dict(my_dataframe)` does this. > `dict(my_dataframe)` does this.

You are right, good to know. I could not find this in the docs. Closing this PR. > `dict(my_dataframe)` does this.

No longer true.