docs, remove 'guifontset' #11708

- remove redundant autocmd list
  This "grouped" list is useless, it only gets in the way when searching
  for event names.
- intro.txt: cleanup
- starting.txt: update, revisit
- doc: `:help bisect`
- mbyte.txt: update aliases 1656367b90. closes #11960
- options: remove 'guifontset'. Why:
  - It is complicated and is used by almost no one.
  - It is unlikely to be implemented by Nvim GUIs (complicated to parse,
    specific to Xorg...).

src/nvim/api/vim.c

@@ -204,9 +204,9 @@ Integer nvim_get_hl_id_by_name(String name)
 ///
 /// On execution error: does not fail, but updates v:errmsg.
 ///
-///  If you need to input sequences like <C-o> use |nvim_replace_termcodes|
-///  to replace the termcodes and then pass the resulting string to
-///  nvim_feedkeys. You'll also want to enable escape_csi.
+/// If you need to input sequences like <C-o> use |nvim_replace_termcodes| to
+/// replace the termcodes and then pass the resulting string to nvim_feedkeys.
+/// You'll also want to enable escape_csi.
 ///
 /// Example:
 /// <pre>