ENH: support pendulum objects
```python
import pendulum
import pandas
pandas.date_range(start=pendulum.now(), end=pendulum.tomorrow())

[1]    56829 segmentation fault  ipython
```
#### Problem description

As `pendulum` claims to inherit from `datetime.datetime`, I wouldn't expect a segfaut to happen, as `date_range` always worked find with `datetime` objects

From [the documentation](https://pendulum.eustace.io/docs/#introduction):
> The Pendulum class is a drop-in replacement for the native datetime class (it is inherited from it).

I could file an issue on the pendulum bug tracker as well, but that's pandas who's segfaulting, so I think you guys would have better tools to understand what's going on.

#### Expected Output

```
DatetimeIndex(['2017-04-12 20:54:52.305104', '2017-04-13 20:54:52.305104'], dtype='datetime64[ns]', freq='D')
```

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Darwin
OS-release: 15.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: fr_BE.UTF-8
LOCALE: fr_BE.UTF-8

pandas: 0.19.2
nose: None
pip: 9.0.1
setuptools: 34.4.1
Cython: None
numpy: 1.12.1
scipy: None
statsmodels: None
xarray: None
IPython: 5.3.0
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: None
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.1.9
pymysql: None
psycopg2: 2.6.2 (dt dec pq3 ext lo64)
jinja2: 2.9.6
boto: None
pandas_datareader: None

</details>
