Implement return rows affected by operation if lastrowid is not set for asyncpg and adopt

[gvbgduh]

It's the continuation of the PR #150 (as this PR only implements for mysql and sqlite) for the ticket #61 to cover other back-ends.

[collerek]

Hi @gvbgduh will you proceed with this issue as you described in #150?

[fgimian]

Please see my comment at #61 (comment) for information on how this can be done for asyncpg. In my personal opinion, I think the two values should be returned separately, via a tuple, nametuple or object. The reason is that both pieces of information are ints, it is not clear with the current implementation whether you're getting back a primary key or a row count.