Range

[tigh-latte]

Add a Range function for ordered traversal.

I know that #8 is already opened and adds an iterator, however, this solution is both simplified and conforms to a pattern already in Golang, sync.Map.Range.

Usage:

om.Range(func(k string, v interface{}) bool {
	fmt.Printf("key=%s, val=%v\n", k, v)
	return true
})

If a user wants to break, then they can just return false from the passed function.