Steven Tran

This PR adds `SetUseNumber` which enables the use of [UseNumber](https://golang.org/pkg/encoding/json/#Decoder.UseNumber) to prevent precision loss when unmarshalling integers. Example usage: ``` func main() { o := orderedmap.New() o.SetUseNumber(true) json.Unmarshal([]byte(`{"x":9007199254740993}`), &o) x,...