Allow selecting struct columns without breaking up the struct

[Learath2]

This feature allows selecting structs without breaking them up. It's useful for types like time.Time, where having it as a selectColumn generates nothing in the marshalled select clause.

[salesforce-cla[bot]]

Thanks for the contribution! Before we can merge this, we need @Learath2 to sign the Salesforce Inc. Contributor License Agreement.

[Learath2]

I did sign the CLA and if I click the link again it says you have already signed the CLA. It seems broken somehow