Support BigInts for 64-bit numbers above 2 ** 53

[ARitz-Cracker]

Numbers >= 2 ** 53 aren't accurate integers in JS. This is why we have BigInts to handle values larger than this. But this library doesn't utilize them at all

[zachasme]

I made a pull request for this (#115) a couple of years ago.

[kkokkojeong]

@mourner
Do you have a plan to support for BigInt(Numbers >= 2 ** 53) ? I'm suffering the same issue ㅠ