First review the `sqlite_sequence` support so that we can still work with
databases that don't have this catalog, which doesn't always exists -- it
might depend on the SQLite version though.
Then while at it use the sql macro to host the SQLite “queries” in their own
files, enhancing the hackability of the system to some degrees. Not that
much, because we have to use a lot of PGRAMA command and then the column
output isn't documented with the query text itself.
