Log Message:
lowdown: update to 0.10.0.

Version 0.10.0, 2021-10-08

Add "flat" OpenDocument output with -Tfodt. This implements the
OpenDocument v1.3 standard, and is readable at least on LibreOffice.
This further implements -Tfodt change tracking in lowdown-diff(1).
It does not support images or definition lists yet.