Handle embedded fields in models

Hi,

Wondering if you'd be interested in the following change to interfaceToModel to handle embedded fields in the model. I moved the field extraction out to its own function and recursively call it for embedded fields. It does not currently handle duplicate fieldnames, I'm not entirely sure how to handle it yet.

I've also changed the comment about how to register the sqlite3 dialect since I spent quite awhile trying to figure out what I did wrong after commenting that one in.

cheers, Ulf