add --bashcompletiondir and --zshcompletiondir (like --emacslispdir) to choose
installation dir for bash/zsh completion files
Make some features optional:
--without-emacs / --with-emacs=no do not install lisp file
--without-bash-completion / --with-bash-completion=no do not install bash
files
--without-zsh-completion / --with-zsh-completion=no do not install zsh files
By default, everything is enabled. You can reenable something with
--with-feature=yes