Instantiate carrier objects on each loop iteration. Add hearing to check...

This eliminates the init() method from Mem(), and does instantiation inside the export loop, same as in your change at https://github.com/Zotero-ODF-Scan/zotero-odf-scan/commit/07b99bf51428c3ddc0ccd5ee72eddc53dec27559.

It also adds "hearing" to the list of legal types.