Multicolumn unique indexes are not handled correctly

[James-REANNZ]

If a unique index contains multiple columns, then all the columns are marked as being independently unique. This leads to incorrect code generation when one of the columns is a foreign key, as it implies a one-to-one relationship.

create table example (
    id                  integer  not null primary key,
    other_id            integer  not null references other(id),
    type                text     not null,

    constraint other_type_unique unique (other_id, type)
);

Leads to code that looks like this:

type otherR struct {
	Example *Example
}

in other.go instead of:

type otherR struct {
	Examples ExampleSlice
}