[XLS] support file object

In Brasil.IO we needed to create the following function to open a XLS file from fobj:

import os
from pathlib import Path
from tempfile import NamedTemporaryFile
import rows

def import_xls(f_obj):
    content = f_obj.read()
    f_obj.seek(0)

    temp_xls = NamedTemporaryFile(suffix='.xls', delete=False)
    temp_xls.write(content)
    temp_xls.close()

    data = rows.import_from_xls(temp_xls)
    temp_file = Path(temp_xls.name)
    os.remove(temp_file)

    return data

We may support it automatically in rows too, so the plugin will have the same interface as the others.

Start by tracing rows.import_from_xls and comparing how the other format plugins handle file objects. The change is complete when XLS input accepts a file object through the same interface as the other plugins, without requiring callers to create a temporary file first.