Markdown writer: better escaping of < and >.

If `all_symbols_escapable` is set, we backslash escape these.
Otherwise we use entities as before.

src/Text/Pandoc/Writers/Markdown.hs

@@ -280,8 +280,12 @@ escapeString :: WriterOptions -> String -> String
 escapeString _  [] = []
 escapeString opts (c:cs) =
   case c of
-       '<'   -> "&lt;" ++ escapeString opts cs
-       '>'   -> "&gt;" ++ escapeString opts cs
+       '<' | isEnabled Ext_all_symbols_escapable opts ->
+              '\\' : '<' : escapeString opts cs
+           | otherwise -> "&lt;" ++ escapeString opts cs
+       '>' | isEnabled Ext_all_symbols_escapable opts ->
+              '\\' : '>' : escapeString opts cs
+           | otherwise -> "&gt;" ++ escapeString opts cs
        _ | c `elem` ['\\','`','*','_','[',']','#'] ->
               '\\':c:escapeString opts cs
        '^' | isEnabled Ext_superscript opts -> '\\':'^':escapeString opts cs

test/writer.markdown

@@ -80,7 +80,7 @@ E-mail style:
 >
 > > nested
 
-This should not be a block quote: 2 > 1.
+This should not be a block quote: 2 \> 1.
 
 And a following paragraph.
 
@@ -580,9 +580,9 @@ AT&T is another way to write it.
 
 This & that.
 
-4 < 5.
+4 \< 5.
 
-6 &gt; 5.
+6 \> 5.
 
 Backslash: \\
 
@@ -604,7 +604,7 @@ Left paren: (
 
 Right paren: )
 
-Greater-than: &gt;
+Greater-than: \>
 
 Hash: \#