BigInt for long

[emilbayes]

Hi!

Can I choose a custom serializer/deserializer for data types? I'm specicially wanting longs to be represented as JS native BigInt type. I'm also happy to provide a PR if this is something you'd want in the module

[michaelwittig]

Hi!

We only have the long2number setting to represent longs as https://www.npmjs.com/package/long

Since we now have BigInt your suggestion makes a lot of sense to use them.

PR is welcome. If possible, the changes should be backward compatible.