Update URLs

* Update mkinitcpio-archiso project link,
* Update code of conduct link,
* Update arch-releng mailing list link,
* Use HTTPS where possible,
* Replace dead link.

CHANGELOG.rst

@@ -241,7 +241,7 @@ Removed
 -------
 
 - Remove all files related to ``mkinitcpio`` integration, as they now live in
-  https://gitlab.archlinux.org/mkinitcpio/mkinitcpio-archiso
+  https://gitlab.archlinux.org/archlinux/mkinitcpio/mkinitcpio-archiso
 
 [57] - 2021-07-30
 =================

README.rst

@@ -139,14 +139,14 @@ Contribute
 
 Development of archiso takes place on Arch Linux' Gitlab: https://gitlab.archlinux.org/archlinux/archiso.
 
-Please read our distribution-wide `Code of Conduct <https://wiki.archlinux.org/title/Code_of_conduct>`_ before
+Please read our distribution-wide `Code of Conduct <https://terms.archlinux.org/docs/code-of-conduct/>`_ before
 contributing, to understand what actions will and will not be tolerated.
 
 Read our `contributing guide <CONTRIBUTING.rst>`_ to learn more about how to provide fixes or improvements for the code
 base.
 
 Discussion around archiso takes place on the `arch-releng mailing list
-<https://lists.archlinux.org/listinfo/arch-releng>`_ and in `#archlinux-releng
+<https://lists.archlinux.org/mailman3/lists/arch-releng.lists.archlinux.org/>`_ and in `#archlinux-releng
 <ircs://irc.libera.chat/archlinux-releng>`_ on `Libera Chat <https://libera.chat/>`_.
 
 All past and present authors of archiso are listed in `AUTHORS <AUTHORS.rst>`_.

configs/releng/syslinux/archiso_head.cfg

@@ -12,7 +12,7 @@ MENU CMDLINEROW 14
 MENU HELPMSGROW 16
 MENU HELPMSGENDROW 29
 
-# Refer to http://syslinux.zytor.com/wiki/index.php/Doc/menu
+# Refer to https://wiki.syslinux.org/wiki/index.php/Comboot/menu.c32
 
 MENU COLOR border       30;44   #40ffffff #a0000000 std
 MENU COLOR title        1;36;44 #9033ccff #a0000000 std

configs/releng/syslinux/archiso_tail.cfg

@@ -7,12 +7,12 @@ MENU LABEL Boot existing OS
 COM32 chain.c32
 APPEND hd0 0
 
-# http://www.memtest.org/
+# https://www.memtest.org/
 LABEL memtest
 MENU LABEL Run Memtest86+ (RAM test)
 LINUX /%INSTALL_DIR%/boot/memtest
 
-# http://hdt-project.org/
+# https://wiki.syslinux.org/wiki/index.php/Hdt_(Hardware_Detection_Tool)
 LABEL hdt
 MENU LABEL Hardware Information (HDT)
 COM32 hdt.c32