better and more correct handling of front matter

ftplugin/markdown.vim

@@ -22,11 +22,6 @@ endif
 function! MarkdownFold()
   let line = getline(v:lnum)
 
-  " Front matter
-  if v:lnum == 1 && line == '---'
-    return ">20"
-  endif
-
   " Regular headers
   let depth = match(line, '\(^#\+\)\@<=\( .*$\)\@=')
   if depth > 0
@@ -43,10 +38,16 @@ function! MarkdownFold()
     return ">2"
   endif
 
+  " Front matter
+  if v:lnum == 1 && line == '---'
+    let b:markdown_frontmatter = 1
+    return ">1"
+  endif
+
   " End of front matter
-  let prevline = getline(v:lnum - 1)
-  if (prevline == '...') && (foldlevel(v:lnum-1) == 20)
-    return '>0'
+  if (line == '...') && b:markdown_frontmatter
+    unlet b:markdown_frontmatter
+    return '<1'
   endif
 
   return "="