Added back to their right place my submodules, but I could not add
Spacemacs as one since submodules from a repository cannot host or be
hosted by another submodule of the same repository.
Emacs-related submodules and files are now hosted in ~/.config/emacs
in prevision for Emacs 27 (for now, ~/.emacs.d is a symlink to this
directory)
Other submodules have been moved to ~/.config in order to clean my
$HOME directory
