Textile reader: don't allow inline formatting to extend over newline.

This matches behavior of RedCarpet, avoids some ugly bugs, and improves
performance.

src/Text/Pandoc/Readers/Textile.hs

@@ -616,7 +616,8 @@ simpleInline border construct = try $ do
   attr <- attributes
   body <- trimInlines . mconcat <$>
           withQuoteContext InSingleQuote
-            (manyTill inline (try border <* notFollowedBy alphaNum))
+            (manyTill (notFollowedBy newline >> inline)
+             (try border <* notFollowedBy alphaNum))
   return $ construct $
         if attr == nullAttr
            then body