Addresses issue #621 (#1181)

* issue#621: html highlighter

* docs for issue#621

* removing windows support for issue#621

Co-authored-by: Tinmarino <tinmarino@gmail.com>

autoload/vimwiki/html.vim

@@ -1879,6 +1879,32 @@ function! s:convert_file(path_html, wikifile) abort
       return ''
     endif
     call vimwiki#path#mkdir(path_html)
+
+    if g:vimwiki_global_vars['listing_hl'] > 0 && has("unix")
+      let i = 0
+      while i < len(html_lines)
+        if html_lines[i] =~ '^<pre .*type=.\+>'
+          let type = split(split(split(html_lines[i], 'type=')[1], '>')[0], '\s\+')[0]
+          let attr = split(split(html_lines[i], '<pre ')[0], '>')[0]
+          let start = i + 1
+          let cur = start
+
+          while html_lines[cur] !~ '^<\/pre>'
+            let cur += 1
+          endwhile
+
+          let tmp = ('tmp'. split(system('mktemp -p . --suffix=.' . type, 'silent'), 'tmp')[-1])[:-2]
+          call system('echo ' . shellescape(join(html_lines[start:cur - 1], '\n')) . ' > ' . tmp)
+          call system(g:vimwiki_global_vars['listing_hl_command'] . ' ' . tmp  . ' > ' . tmp . '.html')
+          let html_out = system('cat ' . tmp . '.html')
+          call system('rm ' . tmp . ' ' . tmp . '.html')
+          let i = cur
+          let html_lines = html_lines[0:start - 1] + split(html_out, '\n') + html_lines[cur:]
+        endif
+        let i += 1
+      endwhile
+    endif
+
     call writefile(html_lines, path_html.htmlfile)
     return path_html . htmlfile
   endif