Revamp display of headings

h1 through h3 are bold, prefixed by a matching number of § characters.
h4 through h6 are italic and indented, but otherwise not distinguished
from each other. In any case, if you're using an h6 you have other
problems.

src/Text/Pandoc/Writers/ANSI.hs

@@ -130,12 +130,12 @@ blockToANSI opts (Header level _ inlines) = do
   contents <- inlineListToANSI opts inlines
   inner <- gets stInner
   return $ header inner level contents $$ D.blankline where
-    header False 1 = (D.flush .  D.bold)
-    header True 1 = (D.underlined . D.bold)
-    header False 2 = ((<> D.literal "  ") . D.bold)
-    header True 2 = D.bold
-    header _ 3 = D.italic
-    header _ _ = id
+    -- hangMark d = D.hang 2 (D.literal "• ") d
+    header False 1 d = D.hang 4 (D.literal "  § ") (D.bold d)
+    header False 2 d = D.hang 4 (D.literal " §§ ") (D.bold d)
+    header False 3 d = D.hang 4 (D.literal "§§§ ") (D.bold d)
+    header False _ d = D.nest 4 (D.italic d)
+    header True _ d = D.bold d
 
 -- The approach to code blocks and highlighting here is a best-effort with
 -- existing tools, and can easily produce results that aren't quite right. Using