Add a way for users to use Number instead of float64

[bterrier]

Right now the JSON is parsed using json.Unmarshal() with no way to customize how it is parsed.

However, for some use cases it could be useful to parse with UseNumber() (https://pkg.go.dev/encoding/json#Decoder.UseNumber) so that it is possible to correctly parse numbers that would not fit in a float64.

On way it could be done would be to replace

func parse(b []byte) (*Node, error) {
	var v interface{}
	if err := json.Unmarshal(b, &v); err != nil {
		return nil, err
	}
	doc := &Node{Type: DocumentNode}
	parseValue(v, doc, 1)
	return doc, nil
}

by something like

func ParseInterface(x interface{}) (*Node, error) {
	doc := &Node{Type: DocumentNode}
	parseValue(v, doc, 1)
        return doc, nil
}

func parse(b []byte) (*Node, error) {
	var v interface{}
	if err := json.Unmarshal(b, &v); err != nil {
		return nil, err
	}
	return ParseInterface(v)
}

so that user can either call Parse() and have the current behavior, or call ParseInterface() after doing their own unmarshalling using their own Decoder.

[crone123]

I have created a pull request for this: #22