- Refactored image path generation into a separate function. ...

- If the description element is missing, @basename is used for the ALT attribute
  in HTML.
- Added check for existence of @basename attribute.

- Added a module to generate errors for obsolete element/attribute usages that ...

might still be in use.
- Moved all deprecated and obsolete items into new "obsolete" module.
- Removed processing code for obsolete child elements of "image".

- Split floating items and images off into separate modules.