Fixes typo in serializer.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Append tags to view.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Add categories view.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>