Allow passing a pop.Model directly

[zepatrik]

Description

I was surprised to figure out I could not pass a pop.Model as the destination. It would be nice to be able to pass that directly and use my own AS name. Here is an example of what I'd like to do:

c.Where("r.subject = ? AND r.skip=FALSE", subject).
   	Where("h.error='{}'").
   	Join("hydra_oauth2_consent_request AS r", "h.challenge = r.challenge").
   	Order("h.requested_at DESC").
   	All(&pop.Model{
   			Value: &rs,
   			As: "h",
   	})

Instead I have to do something like

tn := consent.HandledConsentRequest{}.TableName()

c.Where("r.subject = ? AND r.skip=FALSE", subject).
		Where(fmt.Sprintf("%s.error='{}'", tn)).
		Join("hydra_oauth2_consent_request AS r", fmt.Sprintf("%s.challenge = r.challenge", tn)).
		Order(fmt.Sprintf("%s.requested_at DESC", tn)).
		All(&rs)

I think it is quite easy to implement and can reduce the complexity of writing long queries like the one above.

Expected Behavior

Customize AS through passing a pop.Model.

Actual Behavior

Does not work.