Allow INSERT and UPDATE to reference columns or function results

[jaypipes]

I'd like to allow both the sqlb.Update() and sqlb.Insert() functions to be able to reference another column or the result of a SQL function in their column value lists.

For example, let's say I want to set the created_on column to the result of the NOW() SQL function.

I'd like to be able to do:

vals := map[string]interface{}{
    "name": username,
    "created_on": sqlb.Now(),
}
q := sqlb.Insert(users, vals)
qs, qargs := q.StringArgs()

and have the qs variable contain:

INSERT INTO users (name, created_on) VALUES (?, NOW())