Use uint64 instead of int64

[kzys]

go-hashids provides EncodeInt64 but it actually rejects negative numbers in below. Does it make sense to use uint64, or provides a uint64 variant?

// EncodeInt64 hashes an array of int64 to a string containing at least MinLength characters taken from the Alphabet.
// Use DecodeInt64 using the same Alphabet and Salt to get back the array of int64.
func (h *HashID) EncodeInt64(numbers []int64) (string, error) {
	if len(numbers) == 0 {
		return "", errors.New("encoding empty array of numbers makes no sense")
	}
	for _, n := range numbers {
		if n < 0 {
			return "", errors.New("negative number not supported")
		}
	}

I'm using go-hashids along with hashids' Ruby implementation. In some cases, go-hashids rejects inputs that exceed MaxInt, while the Ruby implementation can handle it because Ruby's Integer can be larger than Go's MaxInt.

I made a fork to workaround the issue and happy to upstream something like this.

https://github.com/kzys/go-hashids/