extradoc.py: Add options -I and -X.
README.org: Adjusted.
extradoc.py: Correct handling of nested #+IF conditionals.
poporg.el: Imply sextuple-quoted for Python strings.
README.org: Adjusted.
poporg.el: Recover the edited region when dwim called in a greyed area.
REAMDE.org: Adjusted.
poporg.el: Exiting an edit, force display within the original file.