Support for collections with frozen types. about gocqlx

[mmatczuk]

With gocql you must implement MarshalUDT and UnmarshalUDT functions to make it work see [1].
With gocqlx, however, you can do that in a very simple way.

// MarshalUDT implements UDTMarshaler.
func (u Address) MarshalUDT(name string, info gocql.TypeInfo) ([]byte, error) {
	f := gocqlx.DefaultMapper.FieldByName(reflect.ValueOf(u), name)
	return gocql.Marshal(info, f.Interface())
}

// UnmarshalUDT implements UDTUnmarshaler.
func (u *Address) UnmarshalUDT(name string, info gocql.TypeInfo, data []byte) error {
	f := gocqlx.DefaultMapper.FieldByName(reflect.ValueOf(u), name)
	return gocql.Unmarshal(info, data, f.Addr().Interface())
}

[1] https://github.com/gocql/gocql/blob/master/udt_test.go

[mmatczuk]

Fixed in #145