Made addSubMenuLink() addSubMenuPages() addSubMenuPage() internal.
* Added: the `columns_{post type slug}` filter for the post type class and deprecated `setColumnHeader()` method.
* Added: the `sortable_columns_{post type slug}` filter for the post type class and deprecated `ettSortableColumns()` method.
- Fixed some docBlock syntax in the inline documentation.
Updated the change log.
Made it use the development version.
Adjusted for the change and made it use the newly introduced filters.
- Removed redundant lines.
- Added comments.
Made it internal.
Made them internal.
Applied the fixes in inline documentation to the documentation pages.