- It is a panel based on Emacs minibuffer, so it works everywhere Emacs
  runs. No xorg/wayland required.
- added zero-input-panel-is-ephemeral variable in zero-input-framework.el

  see its docstring to learn what it is used for.
- this panel is tested works in tty emacs.
- minor, do not update zero-input.el when content would not change.
  updated Makefile and build.py, now build.py will not overwrite zero-input.el
  if content would not change.