Make bindNamed publicly accessible

I wrote a few little functions to mash this library up with the Pipes library, to provide streaming queries through 
its API, and I found that I needed the `bindNamed` function to implement some things, such as:

    queryNamedP :: (MonadSafe m, FromRow a) => Connection -> Query -> [NamedParam] -> Producer a m ()
    queryNamedP conn q ns = bracketIO open' closeStatement each'
        where open' = do s <- openStatement conn q
                         bindNamed s ns
                         return s