BigInt Constructor Support

[mkadirtan]

Thanks a lot for this package. However I gained a huge performance boost if instead of returning hexToDec(hex), BigInt(hex).
For comparison BigInt constructor yields around 0.05 ms consistently. Whereas hexToDec yields around 0.35 ms - 0.9 ms varying randomly. A BigInt constructor with fallback to hexToDec would be great, I can do it if you want to

[s-yadav]

Would you like to create a PR for this?

[mkadirtan]

Sure!