read_excel allows header to be None. (#46)

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.read_excel.html

While the docs are not clear:

> header int, list of int, default 0
> Row (0-indexed) to use for the column labels of the parsed DataFrame. If
> a list of integers is passed those row positions will be combined into a
> MultiIndex. Use None if there is no header.

`header` should be set to `None` if the spreadsheet contains no header row.

> names array-like, default None
> List of column names to use. If file contains no header row, **then you
> should explicitly pass header=None**.

This change makes `header` optional.

Author: aholmes

third_party/3/pandas/io/excel/_base.pyi

@@ -10,7 +10,7 @@ from pandas.util._decorators import Appender as Appender
 from typing import Any, Optional, Sequence, Union
 
 
-def read_excel(io: Any, sheet_name: Optional[Union[str, int, Sequence[Union[str, int]]]] = ..., header: Union[int, Sequence[int]] = ..., names: Optional[Any] = ..., index_col: Optional[Any] = ..., usecols: Optional[Any] = ..., squeeze: bool = ..., dtype: Optional[Any] = ..., engine: Optional[Any] = ..., converters: Optional[Any] = ..., true_values: Optional[Any] = ..., false_values: Optional[Any] = ..., skiprows: Optional[Any] = ..., nrows: Optional[Any] = ..., na_values: Optional[Any] = ..., keep_default_na: bool = ..., verbose: bool = ..., parse_dates: bool = ..., date_parser: Optional[Any] = ..., thousands: Optional[Any] = ..., comment: Optional[Any] = ..., skipfooter: int = ..., convert_float: bool = ..., mangle_dupe_cols: bool = ..., **kwds: Any) -> Any: ...
+def read_excel(io: Any, sheet_name: Optional[Union[str, int, Sequence[Union[str, int]]]] = ..., header: Optional[Union[int, Sequence[int]]] = ..., names: Optional[Any] = ..., index_col: Optional[Any] = ..., usecols: Optional[Any] = ..., squeeze: bool = ..., dtype: Optional[Any] = ..., engine: Optional[Any] = ..., converters: Optional[Any] = ..., true_values: Optional[Any] = ..., false_values: Optional[Any] = ..., skiprows: Optional[Any] = ..., nrows: Optional[Any] = ..., na_values: Optional[Any] = ..., keep_default_na: bool = ..., verbose: bool = ..., parse_dates: bool = ..., date_parser: Optional[Any] = ..., thousands: Optional[Any] = ..., comment: Optional[Any] = ..., skipfooter: int = ..., convert_float: bool = ..., mangle_dupe_cols: bool = ..., **kwds: Any) -> Any: ...
 
 class _BaseExcelReader(metaclass=abc.ABCMeta):
     book: Any = ...