Merge branch 'api'

diff --cc src/catalogue/models/book.py
index 02278de,00921b8..140ba50
--- 1/src/catalogue/models/book.py
--- 2/src/catalogue/models/book.py
+++ b/src/catalogue/models/book.py
@@@ -119,11 -122,8 +122,11 @@@ class Book(models.Model)
          else:
              return ', '.join(self.tags.filter(category=category).values_list('name', flat=True))
  
 +    def tags_by_category(self):
 +        return split_tags(self.tags.exclude(category__in=('set', 'theme')))
 +
      def author_unicode(self):
-         return self.tag_unicode('author')
+         return self.cached_author
  
      def translator(self):
          translators = self.extra_info.get('translators')