DOC: Capitalize docstring summaries of Series
Our standard is to start the docstrings with a capital letter (and finish them with a period).

We'll shortly add a check to make sure that new contributions follow this standard. But before we can do that, we need to fix the many cases that are already wrong.

In this issue we should fix all the cases of methods of Series. This is the command to generate them (which should return nothing after the fix), and the list of current issues.
```
$ ./scripts/validate_docstrings.py --prefix=pandas.Series --errors=SS02
pandas.Series.dtype: Summary does not start with a capital letter
pandas.Series.ftype: Summary does not start with a capital letter
pandas.Series.shape: Summary does not start with a capital letter
pandas.Series.nbytes: Summary does not start with a capital letter
pandas.Series.ndim: Summary does not start with a capital letter
pandas.Series.size: Summary does not start with a capital letter
pandas.Series.strides: Summary does not start with a capital letter
pandas.Series.itemsize: Summary does not start with a capital letter
pandas.Series.base: Summary does not start with a capital letter
pandas.Series.T: Summary does not start with a capital letter
pandas.Series.hasnans: Summary does not start with a capital letter
pandas.Series.flags: Summary does not start with a capital letter
pandas.Series.dtypes: Summary does not start with a capital letter
pandas.Series.ftypes: Summary does not start with a capital letter
pandas.Series.data: Summary does not start with a capital letter
pandas.Series.get_values: Summary does not start with a capital letter
pandas.Series.item: Summary does not start with a capital letter
pandas.Series.argmin: Summary does not start with a capital letter
pandas.Series.argmax: Summary does not start with a capital letter
pandas.Series.dt.round: Summary does not start with a capital letter
pandas.Series.dt.floor: Summary does not start with a capital letter
pandas.Series.dt.ceil: Summary does not start with a capital letter
pandas.Series.to_msgpack: Summary does not start with a capital letter
pandas.Series.sparse: Summary does not start with a capital letter
pandas.Series.transpose: Summary does not start with a capital letter
```

In some cases the problem is that there is a deprecated directive `.. deprecated::` at the beginning of te docstring. This is wrong too, and the deprecation should be after the short summary (the first line/paragraph of the summary).

While this issue is mainly to make the first letter in the summary a capital letter, for the cases where this is fix, would be nice to also add a period at the end of the paragraph, if there is not one already.