Styleframe

* **Added Python 3.10 support**
* Added ability to set individual borders' type via the `border_type` argument
when creating a `Styler` object
* Fixes [GitHub issue 108](https://github.com/DeepSpace2/StyleFrame/issues/108) - Styling and exporting a dataframe that
contains a column called "index"
* Fixes error when attempting to use `best_fit` argument in `StyleFrame.to_excel`
on an empty dataframe [GitHub PR 157](https://github.com/DeepSpace2/StyleFrame/pull/157)

* Added `strikethrough` and `italic` to `Styler`
* Raising `TypeError` in `to_excel` if trying to use a non-openpyxl engine
* Exposing `Exposing StyleFrame.ExcelWriter` and `StyleFrame.read_excel` to the module-level (`styleframe.ExcelWriter`
and `styleframe.read_excel`) to more closely mimic pandas' API
* Fixes [GitHub issue 124](https://github.com/DeepSpace2/StyleFrame/issues/124) - Improved calculation of color luminosity from tint

* **Removed Python 3.4 support**
* **Removed Python 3.5 support**
* **Added Python 3.9 support**
* Allowing `StyleFrame.ExcelWriter` to accept any argument (except for `engine`) that `pandas.ExcelWriter` accepts
* Allowing customizing formats of `date`, `time` and `datetime` objects when creating `Styler` instances
* Fixed rows mis-alignment issue when calling `to_excel` with `header=False` ([GitHub issue 88](https://github.com/DeepSpace2/StyleFrame/issues/88))
* `read_excel` does not accept `sheetname` argument anymore (was deprecated since version 1.6). Use `sheet_name` instead.

* Fixes [GitHub issue 94](https://github.com/DeepSpace2/StyleFrame/issues/94) - Passing `border_type=utils.borders.default_grid` to `Styler`

* Fixes [GitHub issue 81](https://github.com/DeepSpace2/StyleFrame/issues/81) - read excel as template headers height

* Fixed style "shifts" when using `read_style=True` and `header=None` with `StyleFrame.read_excel`. Fixes [GitHub issue 80](https://github.com/DeepSpace2/StyleFrame/issues/80)