Support for OrderPrepend

[arizanovj]

Hi.
First of all thanks for the library. It's quite handy for building complex queries.
I have a use case that I can't produce. I am building keyset pagination and what I need to achieve is the following:
In the models where I need the pagination I pass the pagination struct. So for example in the product model I have this:

func (p *Product) GetProducts(pagination *pagination.Pagination) *[]Product {
	var (
		product  Product
		products []Product
	)
	pagination.PK = "id"
	query := p.Env.QB.From("product").Order(goqu.I("name").Asc()).Prepared(true)

	query = pagination.Paginate(query)
	sql, args, _ := query.ToSql()
}

And this is the the pagination struct which needs to "paginate" the query.

type Pagination struct {
	ID        *uint64 `json:"ID" schema:"ID"`
	PerPage   int64   `json:"perPage" schema:"perPage"`
	Direction string  `json:"direction" schema:"direction"`
	PK        string
	Env       *env.Env
}
func (p *Pagination) Paginate(query *goqu.Dataset) *goqu.Dataset {
	order := query.GetClauses().Order

	if order != nil {
		query.ClearOrder()
	}
	query = query.Order(p.GetOrder())
	if order != nil {
		fmt.Printf("%+v\n", order)
		//orderedExpression := goqu.OrderedExpression{}
		//query = query.GetClauses().Order.Append(order)

		//query = query.OrderAppend(order...)
	}

	if p.ID != nil {
		fmt.Printf("%+v\n", order)
		query = query.Where(p.GetWhere())
	}

	query = query.Limit(uint(p.PerPage))

	if p.Direction == "down" {
		query = p.Invert(query)
	}

	return query
}

func (p *Pagination) GetOrder() goqu.OrderedExpression {
	if p.Direction == "up" {
		return goqu.I(p.PK).Asc()
	} else {
		return goqu.I(p.PK).Desc()
	}
}

So in the paginate function I have this piece of code.

order := query.GetClauses().Order

	if order != nil {
		query.ClearOrder()
	}
	query = query.Order(p.GetOrder())
	if order != nil {
		fmt.Printf("%+v\n", order)
		
		//query = query.GetClauses().Order.Append(order)

		//query = query.OrderAppend(order...)
   }

What I am trying to do is extract the previously set order, add the new order to the *Dataset and append everything else that was previously added. I need this since the order for the primary ID needs to get precedence over the orders of all other columns. Basically what I need is OrderPrepend function which I can't find in the library.

I think I need the following function exposed as public to achieve that. What do you suggest ?

func orderList(vals ...OrderedExpression) ColumnList {..}