Handle backquotes better
Don't fontify a quoted macro since this won't get expanded normally
Merge remote-tracking branch 'georgek/backquotes'

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Refactor backquote handling and text properties.

- add `macrostep-propertize' macro to put text properties on inserted
  text more cleanly

- rename `macrostep-print-sexp' flag to `quoted-form-p' and pass its
  value to recursive calls (so that sub-forms of quoted forms are not
  treated as if evaluated)

- handling of quoted forms could still be improved slightly by
  tracking the level of backquote nesting, but that's pprobably not
  necessary.