(De)serialize 128 bit integers

[AregevDev]

The program crashes when trying to serialize them, complaining i/u128 is not supported
Serde itself already has support for that

[pyfisch]

AFAIK neither the CBOR RFC 7049 nor an extension in CBOR supports 128 bit numbers. (big decimals are supported by the standard but not by this crate) If you need 128 bit integers I suggest to serialize them as a slice.

[AregevDev]

Oh, didn't know that, started working on PR, never mind

[dtolnay]

The program crashes when trying to serialize them

Is this a crash or does serde_cbor return an error?

[AregevDev]

cbor returns an error

[nhynes]

related: #145

[surban]

MsgPack stores u128/i128 as a byte array. I think it would be a simple fix for serde_cbor to do the same?