tidy-up: miscellaneous

- tool_bname: scope an include.
- `endif` comments.
- Markdown fixes.
- comment tidy-ups.
- whitespace, newlines, indent.

Closes #20309

lib/memdebug.c

@@ -115,6 +115,7 @@ static void curl_dbg_cleanup(void)
   }
 #endif
 }
+
 #ifdef USE_BACKTRACE
 static void error_bt_callback(void *data, const char *message,
                               int error_number)