Add `Series.todict()` for consistency?
#### Problem description

Hello all! Hope this is the right avenue to post this.

So Series has functions `to_list()` and `to_dict()`,  with the underscore in the middle. There's also `tolist()` w/o the underscore, but not `todict()`. Don't suppose there's any harm in extending the API to allow the latter?

#### Code Sample

```python
In [1]: import pandas as pd             

In [2]: pd.__version__                  
Out[2]: '0.25.3'

In [3]: srs = pd.Series()               

In [4]: srs.to_dict()                   
Out[4]: {}

In [5]: srs.to_list()                   
Out[5]: []

In [6]: srs.tolist()
Out[6]: []

In [7]: srs.todict()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-7-6908392d3852> in <module>
----> 1 srs.todict()

~/miniconda3/lib/python3.7/site-packages/pandas/core/generic.py in __getattr__(self, name)
   5177             if self._info_axis._can_hold_identifiers_and_holds_name(name):
   5178                 return self[name]
-> 5179             return object.__getattribute__(self, name)
   5180 
   5181     def __setattr__(self, name, value):

AttributeError: 'Series' object has no attribute 'todict'
```