Man reader: Nicer looking "skipped content" report.

Just give the macro name, which users will recognize,
rather than the internal token.

src/Text/Pandoc/Readers/Man.hs

@@ -561,5 +561,7 @@ parseSkipMacro :: PandocMonad m => ManParser m Blocks
 parseSkipMacro = do
   pos <- getPosition
   tok <- mmacroAny
-  report $ SkippedContent (show tok) pos
+  case tok of
+    MMacro mkind _ -> report $ SkippedContent ('.':mkind) pos
+    _              -> return ()  -- shouldn't happen
   return mempty