Lines in the docs files were manually adjusted to conform to the
79 columns limit per line (plus newline), improving readability and
consistency across the content.
Raising DatabaseError directly made it harder than it should to
differentiate between IntegrityError when a forced update resulted in no
affected rows.
Introducing a specialized exception allows for callers to more easily
silence, log, or turn them update failures into user facing exceptions
(e.g. 404s).
Thanks Mariusz for the review.
