ODT to PEF script

This is a great feature that could be achieved with relatively little effort because all *-to-pef scripts are based on the same "XML/CSS to OBFL to PEF" pipeline. The only additional thing needed would be a conversion from .odt file to flat XML. Developing a style sheet is ultimately the responsibility of the user, like is also the case for the other PEF scripts.

An alternative is of course to go through via HTML, but this requires knowledge of the ODT to HTML conversion in order to develop a style sheet, while a direct conversion only requires knowledge of the ODT format itself.

With an ODT to PEF script, the OpenOffice plugin [odt2braille](http://odt2braille.sourceforge.net), which has become abandonware but still has many users, could be replaced with Pipeline 2, or it could be revived and use Pipeline 2 under the hood (would also require https://github.com/daisy/pipeline-tasks/issues/99).