minor suggestion:  fetchcol() method

You've got:

- `fetchval` for scalars
- `fetchrow` for a horizontal list of values
- `fetch` for a list of list of values

But I don't see a convenience method for returning a vertical list of values — such as when selecting a single column.

(In this case, I think returning a plain old list of values would be more useful than a list of single-value Records.)