Update to 2.04

Upstream changes:
2.04      2021-08-06 12:28:31Z
    [ENHANCEMENTS]
    - Add a head() method to allow relative URLs (GH#321) (Julien Fiegehenn)

    [DOCUMENTATION]
    - Document that form_id() accepts an id, not a name (GH#319) (Olaf Alders)

(wen)