Markdown writer: Use setext headers for levels 1-2.

src/Text/Pandoc/Writers/Markdown.hs

@@ -233,17 +233,15 @@ blockToMarkdown _ HorizontalRule =
 blockToMarkdown opts (Header level inlines) = do
   contents <- inlineListToMarkdown opts inlines
   st <- get
-  -- use setext style headers if in literate haskell mode.
-  -- ghc interprets '#' characters in column 1 as line number specifiers.
-  if writerLiterateHaskell opts || stPlain st
-     then let len = offset contents
-          in  return $ contents <> cr <>
-                       (case level of
-                             1  -> text $ replicate len '='
-                             2  -> text $ replicate len '-'
-                             _  -> empty) <> blankline
-     else return $
-       text ((replicate level '#') ++ " ") <> contents <> blankline
+  return $ case level of
+            1 -> contents <> cr <> text (replicate (offset contents) '=') <>
+                  blankline
+            2 -> contents <> cr <> text (replicate (offset contents) '-') <>
+                  blankline
+            -- ghc interprets '#' characters in column 1 as linenum specifiers.
+            _ | stPlain st || writerLiterateHaskell opts ->
+                contents <> blankline
+            _ -> text (replicate level '#') <> space <> contents <> blankline
 blockToMarkdown opts (CodeBlock (_,classes,_) str)
   | "haskell" `elem` classes && "literate" `elem` classes &&
     writerLiterateHaskell opts =