Implement definition data for -tfodt.
Implement definition data for -tfodt.

Add support for -tfodt images and fix definitions.

This makes sure to reset definition list offsets and re-adds the
paragraph break for definitions.

It also adds support for external -tfodt images.  These are
dimensionless unless the image sizes are specifically given.

kristapsdz/lowdown,kristapsdz/lowdown,kristapsdz/lowdown