configure: add options to disable emacs/zsh/bash and choose install dir.

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