Also include missing changes from:
https://github.com/vim/vim/commit/06d2d38ab7564e1f784b1058a4ef4580cd6d1810
https://github.com/vim/vim/commit/26852128a2b713ef49341a0c18daba928444e7eb

- :Man with no arguments opens the manapage for the
  <cWORD> (man buffers) or <cword> (non-man buffers).
- remove now irrelevent comment about -P flag

- fix synopsis highlighting in other locales. Cannot always rely on the first
  line for the section in some locales; instead, use the file path and
  explicitly set b:man_sect to the actual section.
- eliminate separate s:man_args function
- simplify logic: do not reuse buffer content
- introduce b:man_default_sects Fixes #5233
- introduce <Plug>(man_vsplit), <Plug>(man_tab)
- simplify regexps

Closes #5235

To healthcheck the "foo" plugin:
    :CheckHealth foo
To healthcheck the "foo" and "bar" plugins:
    :CheckHealth foo bar
To run all auto-discovered healthchecks:
    :CheckHealth

- Overlay markdown syntax/filetype, don't invent new filetypes/syntaxes.
- migrate s:check_ruby()
- s:indent_after_line1
- Less-verbose output

- Use execute() instead of redir
- Fixed logic on suboptimal pyenv/virtualenv checks.
- Move system calls from strings to lists. Fixes #5218
- Add highlighting
- Automatically discover health checkers
- Add tests

Helped-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Helped-by: Tommy Allen <tommy@esdf.io>

Closes #4932

With -count, if the first argument is a number, it is made available
with <count>. Problem is, there is always a default count it is impossible
to tell whether the user set it.

Since v:count and v:count1 still work with 'keywordprg', -count is
unnecessary. But 'keywordprg' still calls ':Man' with a count prefixed.
So it must still accept a count in the line number position, but not consume
the first argument. This is done with -range.

Fixes #5202.

Regression from #5168. Also changed the Man command's nargs to '+' so
that man#open_page does not need to handle 0 arguments, because that
will never occur.

- Since the names are set and ':vsplit printf(3)' work, there is no need
to unlist them.