prog: markdown-mode doesn't like electric-indent-mode
prog: disable electric-indent-mode locally for some modes

electric-indent-mode is a global minor mode. We need to use specific
steps to disable it locally. See:
  http://stackoverflow.com/questions/21182550/how-to-turn-of-electric-indent-mode-for-specific-major-mode
prog: really disable-electric-indent-mode on selected modes

Some of them are not derived from prog-mode, let's enumerate them and
add them to the appropriate hooks.