doc/vim_diff.txt: formatting

- backticks in Vim help docs are supported by even the default
  colorscheme; we should start using them for technical identifiers
  instead of quotation marks.
- prefer judicious indentation to gratuitous bullets

Helped-by: Michael Reed <m.reed@mykolab.com>

runtime/doc/vim_diff.txt

@@ -21,9 +21,9 @@ these differences.
 ==============================================================================
 1. Configuration					    *nvim-configuration*
 
-- Use ".nvimrc" instead of ".vimrc" for storing configuration.
-- Use ".nvim" instead of ".vim" to store configuration files.
-- Use ".nviminfo" instead of ".viminfo" for persistent session information.
+- Use `.nvimrc` instead of `.vimrc` for storing configuration.
+- Use `.nvim` instead of `.vim` to store configuration files.
+- Use `.nviminfo` instead of `.viminfo` for persistent session information.
 
 ==============================================================================
 2. Option defaults					  *nvim-option-defaults*
@@ -49,27 +49,27 @@ are always available and may be used simultaneously in separate plugins.  The
 
 See |nvim-intro| for a list of Nvim's largest new features.
 
-Meta key chords are recognized (even in the terminal).
-- <M-1>, <M-2>, ...
-- <M-BS>, <M-Del>, <M-Ins>, ...
-- <M-/>, <M-\>, ...
-- <M-Space>, <M-Enter>, <M-=>, <M-->, <M-?>, <M-$>, ...
+Meta-key chords are recognized (even in the terminal).
+  <M-1>, <M-2>, ...
+  <M-BS>, <M-Del>, <M-Ins>, ...
+  <M-/>, <M-\>, ...
+  <M-Space>, <M-Enter>, <M-=>, <M-->, <M-?>, <M-$>, ...
 
-CTRL-SHIFT-... key chords are distinguished from CTRL-... variants (even in
+`CTRL-SHIFT-...` key chords are distinguished from `CTRL-...` variants (even in
 the terminal).
-- <C-Tab>, <C-S-Tab>
-- <C-BS>, <C-S-BS>
-- <C-Enter>, <C-S-Enter>
+  <C-Tab>, <C-S-Tab>
+  <C-BS>, <C-S-BS>
+  <C-Enter>, <C-S-Enter>
 
 Events:
-- |TabNew|
-- |TabNewEntered|
-- |TabClosed|
+  |TabNew|
+  |TabNewEntered|
+  |TabClosed|
 
 Highlight groups:
-- |hl-EndOfBuffer|
-- |hl-TermCursor|
-- |hl-TermCursorNC|
+  |hl-EndOfBuffer|
+  |hl-TermCursor|
+  |hl-TermCursorNC|
 
 ==============================================================================
 5. Missing legacy features				 *nvim-features-missing*
@@ -89,39 +89,42 @@ planned for the current milestone.
 
 These features are in Vim, but have been intentionally removed from Nvim.
 
-Vi-compatible mode
-- ":set nocompatible" is ignored
-- ":set compatible" is an error
+Vi-compatible mode:
+  ":set nocompatible" is ignored
+  ":set compatible" is an error
 
-Ed-compatible mode
-- ":set noedcompatible" is ignored
-- ":set edcompatible" is an error
+Ed-compatible mode:
+  ":set noedcompatible" is ignored
+  ":set edcompatible" is an error
 
-'ttyfast'
-- ":set ttyfast" is ignored
-- ":set nottyfast" is an error
+'ttyfast':
+  ":set ttyfast" is ignored
+  ":set nottyfast" is an error
 
-EBCDIC support
+Encryption support:
+  'cryptmethod'
+  'key'
 
-8.3 filesystem support
-- 'shortname'
+MS-DOS support:
+  'bioskey'
+  'conskey'
 
-Encryption support
-- 'cryptmethod'
-- 'key'
+Other options:
+  'shortname'
+  'shelltype'
+  'textauto'
+  'textmode'
 
-MS-DOS support
-- 'bioskey'
-- 'conskey'
+Other commands:
+  :fixdel
+  :mode no longer accepts an argument
+  :shell
 
-'shelltype'
-":shell"
-":mode", no longer accepts an argument
-'textauto'
-'textmode'
+Other compile-time features:
+  EBCDIC
 
 "Easy mode" (eview, evim, nvim -y)
-"(g)vimdiff" (solely an alias for (g)nvim -d, i.e. |diff-mode|)
+"(g)vimdiff" (alias for "(g)nvim -d" |diff-mode|)
 "Vi mode" (nvim -v)
 
 The ability to start nvim via the following aliases has been removed in favor