insert and delete no longer return values by default

Added insert-returning and delete-returning with the corresponding * fns for when people want it.

You'll want to bump the API for this.

Fixes:

https://github.com/korma/Korma/issues/70

and

https://github.com/korma/Korma/issues/123

I'm open to variations on this theme, but it's better/more common defaults and safer. Makes the concept available at the macro and function query generation levels of the API.