`pretext inspect` or similar

[oscarlevin]

In addition to pretext validate (#29), it would be nice to have an easy way to check for "mistakes" the author might have made. For example, an image without a description. Perhaps this could go into the validation-plus stylesheet (if it's not there already?) or could be a new stylesheet. Sort of an author's tools suite to help improve the quality of a book.

What else should this include?

• Terms without an index entry
• Theorems, figures, latex-images, etc without an xml:id

[davidfarmer]

Sections other divisions which will get their own web page, which do not have an xml:id (or whatever it is that goes into the URL).