Support for named parameters

[newhoggy]

This will allow code like this to be written:

    let sql =
            Text.unlines
                [ "UPDATE pairs "
                , " SET value = :value"
                , " WHERE key = :key"
                ]

    encodedParams <-
        pure $
            mconcat
                [ ENC.encode (ENC.column (EP.named "value" EP.text)) value
                , ENC.encode (ENC.column (EP.named "key" EP.key)) key
                ]

    void $
        newExecuteStatement sql
            <&> the @"database" ?~ "my_database"
            <&> the @"parameters" ?~ fmap toSqlParameter (ENC.unEncodedParams encodedParams [])
            >>= sendAws