allout.el: Summary - migrate to defining allout mode using

allout.el: Summary - migrate to defining allout mode using
define-minor-mode instead of defun.  Significantly clean-up internal keymap
provisions, refactoring a bit and removing a lot of accumulated cruft.

allout-mode-map is now a keymap by virtue of being an defalias to
allout-mode-map-value, which contains the actual keymap structure.

(allout-mode): Use define-minor-mode rather than defun.  Remove
now-unnecessary minor-mode setup activities from the body.  Specify :keymap
as allout-mode-map so the minor-mode-map-alist entry will be
'(allout-mode . allout-mode-map) - see allout-mode-map-value, below.
Adjust docstring to track changes.
(allout-minor-mode): Remove this defalias, now that we're using
define-minor-mode.
(allout-mode-map): Set value to be 'allout-mode-map.  The actual keymap
is allout-mode-map-value, via defalias.
(allout-mode-map-value): The variable holding the actual mode keymap
structure, by virtue of defalias from allout-mode-map.
(allout-compose-and-institute-keymap): Renamed from allout-bind-keys, and
including the binding-composition functionality of the former
produce-allout-mode-map and allout-setup-mode-map.
(allout-institute-keymap): Take over the "setup" part of the former
allout-setup-mode-map.  Reassign allout-mode-map-value value and update the
defalias.
(allout-command-prefix) (allout-prefixed-keybindings)
(allout-unprefixed-keybindings): Use allout-compose-and-institute-keymap to
process the bindings.
(allout-unprefixed-keybindings): Remove extraneous '?' question marks.
(allout-prefixed-keybindings): Elide binding to (prefixed) \C-h - user can
customize if they want to use that binding.  Bind allout-copy-topic-as-kill
to (prefixed) \M-k.  Bind allout-up-current-level to (prefixed) \C-u.  (I
think i mistakenly elided that, previously, instead of the one for \C-h.)
(allout-hotspot-key-handler): Remove attempt to resolve the key through the
literal key-string lookup on allout-keybindings-list.  That probably hasn't
worked for a Long Time, and removal of allout-keybindings-list further
simplifies the keybindings situation.
(allout-pre-command-business): Use allout-mode-map-value instead of
allout-mode-map.
(allout-preempt-trailing-ctrl-h): Remove.  The user can customize the
bindings if they want to use a keybinding having a trailing \C-h.  No
deprecation needed since this feature was never in a release.
(allout-keybindings-list): Remove.  It's not been useful for a while.  (See
allout-hotspot-key-handler changes, above.)
(produce-allout-mode-map): Remove.  Consolidate into
allout-compose-and-institute-keymap.
(allout-mode-map-adjustments): Remove.  No longer necessary with removal of
allout-preempt-trailing-ctrl-h.
(allout-setup-mode-map): Remove.  Consolidate into
allout-compose-and-institute-keymap and allout-institute-keymap.