Prefer font-lock-flush to font-lock-fontify-buffer

On later emacs versions, font-lock-fontify-buffer less unsuitable for
emacs lisp code.
Rename internal variables to use "--" convention
Improve docstring for minor-mode definition.

"Toggle minor mode" is not undescriptive, it is better to copy the
docstring from package description.
Fix buffer corruption when buffer is saved.

Lisp code uses point motion just like the user, and needs to see exact
buffer contents.

This change breaks the "kick-point" mechanism, so it no longer
works. Buffer save corruption is the worse alternative, so it is okay to
break the kick-point thing instead.
Make form-feed lines clickable: hide/show sections

Code sections between consecutive form-feeds will be hidden/shown when
the top form-feed's line is clicked. The comments just after the line
function are shown as a header for the hidden section.