minor suggestion: fetchcol() method

[ofer-pd]

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.)