Convert nested json objects correctly to CSV

Created by: plipp

Before this fix, nested json objects just have been skipped, when converting to csv. With this fix they are converted as follows:

[
    {
        "text": "Chicago Reader", 
        "float": 1.0, 
        "datetime": "1971-01-01T04:14:00", 
        "boolean": true,
        "nested": {
          "time": "04:14:00",
          "nested": {
            "date": "1971-01-01",
            "integer": 40
          }
        }
    }, ...]

csv

text,float,datetime,boolean,nested/time,nested/nested/date,nested/nested/integer
Chicago Reader,1.0,1971-01-01T04:14:00,True,04:14:00,1971-01-01,40