add capability to pass options to to_csv method

[iainsgillis]

On Python 3.10 and 3.11, an upstream bug in pandas causes a failure when serializing a dataframe to csv when there's a null byte in the dataframe.

This pull request leaves the default behaviour alone, but gives users the options to modify pd.DataFrame.to_csv behaviour, including fixing that issue with the escapechar parameter.

See pandas-dev/pandas#47871

If anyone encounters this issue, an alternative is to monkeypatch this socrata-py library. Example follows:

import sys
if sys.version_info >= (3, 10):
    from socrata.sources import Source

    def patched_df(self, dataframe, **kwargs):
        print("using monkeypatched function: see https://github.com/pandas-dev/pandas/issues/47871")
        s = io.StringIO()
        pd_to_csv_params = kwargs.pop("pd_to_csv_params", {"escapechar": "\\"})
        dataframe.to_csv(s, index=False, **pd_to_csv_params)
        return self._chunked_bytes(bytes(s.getvalue().encode()), "text/csv", **kwargs)

    Source.df = patched_df