Option for showing length of series
#### Code Sample, a copy-pastable example if possible

```python
pd.Series(range(10))
```
#### Problem description

There is a option `display.show_dimensions` which allow show the dimension of a `DataFrame`, while it would be useful if the length of a `Series` can be set to show when the index is not a range list.

#### Expected Output
```
0    0
1    1
2    2
3    3
4    4
5    5
6    6
7    7
8    8
9    9
dtype: int64

[10 elements/items/or something else...]
```
#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Darwin
OS-release: 16.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.2
nose: 1.3.7
pip: 9.0.1
setuptools: 34.3.3
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
statsmodels: 0.8.0
xarray: 0.9.1
IPython: 5.3.0
sphinx: 1.5.3
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: 1.2.0
tables: None
numexpr: 2.6.2
matplotlib: 2.0.0
openpyxl: 2.4.5
xlrd: None
xlwt: None
xlsxwriter: 0.9.6
lxml: 3.7.3
bs4: 4.5.3
html5lib: 0.999999999
httplib2: None
apiclient: None
sqlalchemy: 1.1.7
pymysql: None
psycopg2: None
jinja2: 2.9.5
boto: None
pandas_datareader: 0.3.0.post
</details>
