Support por python object CSV serialization in python 2
Let's say we have a file with 2 json encoded rows that we turn into a DataFrame:

```
{"first_name":"Manuel", "last_name":"Garrido Peña","experience":[{"name":"Peña Industries", "start":"May 2014"}]}
{"first_name":"Ana", "last_name":"Cañón", "experience":[{"name":"Cañón technologies","start":"April 2016"}]}
```

If one of the fields in a dataframe is a python object  ( e.g. a dictionary) with unicode strings on it, the 
output of `df.to_csv(NAME, encoding='utf8', index=False) is different with Python2 than with Python3.

```
#python2 output
experience,first_name,last_name
"[{u'start': u'May 2014', u'name': u'Peña Industries'}]",Manuel,Garrido Peña
"[{u'start': u'April 2016', u'name': u'Cañón technologies'}]",Ana,Cañón

#python3 output (expected)
experience,first_name,last_name
"[{'name': 'Peña Industries', 'start': 'May 2014'}]",Manuel,Garrido Peña
"[{'name': 'Cañón technologies', 'start': 'April 2016'}]",Ana,Cañón
```

Basically, it would make sense to be able to read back the `experience` field on that csv (maybe with a safe_eval?), and the unicode flags make it very hard to parse.

The files (and versions) for this example can be found on [this gist](https://gist.github.com/manugarri/4c0d68f9c2c8434654402e6053620b68)
