Sync with new org-export-to-file and org-export-to-file

As of 6f55864f20 (after 8.0.7 and before 8.1) in org-mode,
org-export-to-file and org-export-to-file changed its argument.  New
functions takes async as the first optional argument, which enables
backends to remove its own async handling.
Make alist of list bullets instead of hardcode

Split the list bullet data and list header generator function so that
code itself become generic and does not depends on any data.