(hi-lock-highlight-range): New variable.

(hi-lock-highlight-range): New variable.
(hi-lock-mode, hi-lock-unface-buffer): Call font-lock-fontify-buffer
only if font-lock-fontified is non-nil.  Remove overlays.
(hi-lock-set-pattern): Call font-lock-fontify-buffer if
font-lock-fontified is non-nil, otherwise use overlays (instead of
text properties).
(hi-lock-string-serialize-hash, hi-lock-string-serialize-serial):
New variables.
(hi-lock-string-serialize) New function.