Markdown reader: fixed parsing bug with macros.

Previously macro definitions in indented code blocks
were being parsed as macro definitions, not code.

src/Text/Pandoc/Readers/Markdown.hs

@@ -484,7 +484,6 @@ block = do
   res <- choice [ mempty <$ blanklines
                , codeBlockFenced
                , yamlMetaBlock
-               , guardEnabled Ext_latex_macros *> (macro >>= return . return)
                -- note: bulletList needs to be before header because of
                -- the possibility of empty list items: -
                , bulletList
@@ -494,6 +493,7 @@ block = do
                , htmlBlock
                , table
                , codeBlockIndented
+               , guardEnabled Ext_latex_macros *> (macro >>= return . return)
                , rawTeXBlock
                , lineBlock
                , blockQuote