Work without a serializer

[iamkisly]

Hey. I scanned the code, and I liked it. But I can not find the opportunity to work without a serializer with byte array. Please add this low-level function.

[erictuvesson]

We have talked about this before, probably in discord. @MarkioE said he was playing around with a good solution for it, but I think other things got in the way.

[mingyangzhu]

Most of the time we need a custom packet format，so get raw byte data is necessary. （eg: iot）