Tksheet

Fixed:
- `display_columns()` no longer redraws if `deselect_all` is `True` even when `redraw` is `False`
- `extra_bindings()` cell editors carrying out cell edits even if validation function returns `None`
- Index and header alignments wrongly associated with column and row alignments if `align_header`/`align_index` were `False`
- Undo drag and drop wrong position if columns move back to higher index
- Error when shift b1 press in headers/index while using extra bindings

Changed:
- Internal variable name `data_ref` to `data`
- `get_currently_selected()` and `currently_selected()` see documentation for more information
- The way `extra_bindings()` + `begin_edit_cell` works, now if `None` is returned then the cell editor will not be opened
- Paste repeats when selection box is larger than pasted items and is a multiple of pasted box
- `move_row()`/`move_column()` now internally use `move_rows()`/`move_columns()`
- `black` theme text to be a lot brighter

Added:
- Spacebar to edit cell keys
- Function `open_cell()` which uses currently selected box and mouse event
- Function `data` see the documentation for more info
- Functions `get_cell_alignments()`, `get_row_alignments()`, `get_column_alignments()`, `reset_all_options()`, `delete_out_of_bounds_options()`
- Functions `move_columns()`, `move_rows()`

- Deprecate functions `display_subset_of_columns()`, `displayed_columns()`
- Change `get_text_editor_value()` function argument `destroy_tup` to `editor_info`
- Change `display_columns()` function argument `indexes` to `columns`
- Change `display_columns()` function argument `enable` to `all_columns_displayed`
- Change some internal variable names
- Remove all calls to `update()` from `tksheet`
- Fix row index `"e"` text alignment bug
- Fix checkbox text not showing in main table when not using west alignment
- Fix `total_rows()` bug
- Fix dropdown arrow being asymmetrical with different font sizes
- Fix incorrect default headers while using hidden columns
- Fix issue with `get_sheet_data()` if including index and header not putting a corner cell in the top left
- Modify redrawing code, slightly improve redrawing efficiency in some scenarios
- Add dropdown boxes, check boxes and cell editing to index
- Add options `edit_cell_validation` which is an option for `extra_bindings`, see the documentation for more info
- Add function `yield_sheet_rows()` which includes default index and header values if using them
- Add function `hide_columns()` which allows input of columns to hide, instead of columns to display
- Add functions related to index editing, checkboxes and dropdown boxes
- Add default argument `show_default_index_for_empty`
- Add `Edit header` option to in-built right click menu if both are enabled
- Add `Edit index` option to in-built right click menu if both are enabled
- Add `Edit cell` option to in-built right click menu if both are enabled
- Documentation updates

- Fix bugs with functions `readonly_header()`, `checkbox()` and `header_checkbox()`
- Clarify table colors documentation