Enable customization of 'row-reader in cl-dbi as it is in cl-postgres

[thijs]

In cl-postgres you can do

(prepare-query connection "test-bool" "select $1" '(t))
(exec-prepared connection "test-bool" '(nil) 'list-row-reader)

so that you can specify how you want the results to be transformed for your use. There are a few supplied (list-row-reader as here, and there are more), but you can also create and provide your own.

I was disappointed to see that in cl-dbi this functionality is not utilized. In execute-using-connection the call to exec-prepared has an inline hard-coded row-reader implementation.

I'd like to request this be changed so that the row-reader is user-settable.

I might actually take a stab at creating a pull request for this, but time at the moment is short...