bug#36500: 26.2; Minor mode doc strings - say what the current mode-variable value is

[Drew Adams <drew.adams@oracle.com>]

Apologies if this enhancement request has been proposed before.
It seems like it might have been, as it's a pretty obvious
possibility.

Suggestion:

Have the automatically provided part of a minor-mode doc string, from
`define-minor-mode' do the following (or at least some of it):

1. Mention the mode variable (typically the same name as the mode,
   but in any case the name is known to `define-minor-mode').
   (The doc string currently mentions the keymap, but not the var.)

2. Show the current value of the variable, just as we do for the keymap.
   If undefined so far then say so, just as we do for the keymap.

3. Say whether the variable is global (an option, customizable), or
   buffer-local.

4. Maybe mention that the variable is set/reset automatically when you
   toggle the mode.  If the var is global mention that you can set/reset
   it manually using Customize.

5. Any particularities, e.g. from using `:variable' should be taken into
   account, so the doc string is correct for all cases.



In GNU Emacs 26.2 (build 1, x86_64-w64-mingw32)
 of 2019-04-13
Repository revision: fd1b34bfba8f3f6298df47c8e10b61530426f749
Windowing system distributor `Microsoft Corp.', version 10.0.17134
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''