Introduce some new template functions for archive titles and descript

%1$s besuchenIntroduce some new template functions for archive titles and descript

* `get_the_archive_title()` and `the_archive_title()` for returning/displaying the title of the current term, date, post type, post format, or author archive.
* `get_the_archive_description()` and `the_archive_description()` for returning/displaying the description associated with the current term archive.