Doxygen: fix broken link in freecadweb.org/api page + update all links to https://
Doxygen: fix broken link in freecadweb.org/api page + update all links to https://

Fixes #3442 (https://freecadweb.org/tracker/view.php?id=3442)
Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master