Styleframe

* Fixed a "'column' is out of columns range" error when settings a column's width if dataframe has more than 26 columns.

* Hotfix: Fixed typo in setup.py

* **Change supported versions of openpyxl to >= 2.5**
* Changed `use_openpyxl_styles` argument default value to `False` in `StyleFrame.read_excel`.

* Fixed an issue that prevented reading files which used certain theme colors.

* Reading columns' widths and rows' heights when passing `read_style=True` to `read_excel`.
* Added support for named indexes.
* Added `style_index_header` argument to `apply_headers_style`.
* Added support for pandas <= 0.23.4

* **Added Python 3.7 support**
* Added support for pandas <= 0.23.1
* Added dt and str accessors to Series
* Added support for passing an integer (sheet index) as `sheet_name` to `StyleFrame.read_excel`
* `StyleFrame.read_excel` `sheetname` argument changed to `sheet_name`. Using `sheetname` is still allowed but will
show deprecation warning.
* Added `Styler.combine` method.
* Added `utils.number_formats.decimal_with_num_of_digits` method.
* Added `overwrite_default_style` argument to `StyleFrame` methods `apply_style_by_indexes` and `apply_column_style`