This is only the endpoint, it does nothing yet.

This reverts commit 29ee1972.

It introduces a bug, it should not be merged.

Order of authors, date, source doesn't matter and we can interleave contents.

This has couple of drawbacks:
- we use postgres-simple and a raw sql query, opaleye would be better
I guess
- there is a hack for empty query, this should be replaced by
removing the WHERE clause in this case