Minor improvements to ch 6 & 7

The first and the third commit are my changes. In the first commit I give an example of using a query criteria in update_or_insert.
In the third commit, I explain how to use IS_IN_SET to force completion of checkbox, which I think is common enough to deserve a mention in the book.
The middle commit is a synchronisation of changes back to my repository from upstream. It shouldn't be there.