Update DataFrame.to_feather() docstring/api documentation and deprecate fname argument.

[simonjayhawkins]

Code Sample, a copy-pastable example if possible

This code works.

import pandas as pd
import pandas.util.testing as tm
from io import BytesIO

df = pd.DataFrame({"a": [1, 2, 3], "b": list("abc")})

buf = BytesIO()
df.to_feather(fname=buf)
result = pd.read_feather(path=buf)

tm.assert_frame_equal(result, df)

Problem description

Documentation doesn't mention accepting a buffer.

    def to_feather(self, fname):
        """
        Write out the binary feather-format for DataFrames.

        Parameters
        ----------
        fname : str
            String file path.
        """

Expected Output

change argument name to better reflect types accepted and be consistent with other io methods.

would need to deprecate fname argument.

Output of pd.show_versions()

[paste the output of pd.show_versions() here below this line]