Misc cleanup.

Misc cleanup.
(hide-ifdef-mode-submap): Put the def in the defvar.
Use substitute-key-definition.
(hide-ifdef-mode): Use define-minor-mode.
(hif-outline-flag-region): Remove.
(hif-show-all): Define in terms of hif-show-ifdef-region.
(hif-after-revert-function): Rename from hif-before-revert-function.
(hide-ifdef-region, hif-show-ifdef-region): Use overlays.
(hif-tokenize): Use with-syntax-table.
(hif-make-range): Use `else' also for `else-p'.
(hif-range-else-p): Remove.
(hif-find-range): Simplify.
(hif-hide-line): Don't bother preserving buffer-modified-p.
(hide-ifdefs, show-ifdefs, hide-ifdef-block, show-ifdef-block):
Don't use selective-display and inhibit-read-only.