Currently, errors produced by this package implement fmt.Formatter with special support for the "%+v" format. We should consider removing this support, since it doesn't actually add any information (which is typically the purpose of the + flag).

err := multierr.Append(errors.New("foo"), errors.New("bar"))
fmt.Println(err.Error())
// foo; bar
fmt.Printf("%v\n", err)
// foo; bar
fmt.Printf("%+v\n", err)
// the following errors occurred:
//  - foo
//  - bar

This came up because it makes logging these errors with zap particularly verbose - see post-merge discussion on uber-go/zap#460.