Feature Request: ability to update xxh32 state

[warmwaffles]

I have a use case where I need to accumulate data into the 4 vectors for state.

I'd love to be able to do something like this

xxh = XXHash.XXH32.init(123)
hexdigest = 
  xxh
  |> XXHash.XXH32.update("foo")
  |> XXHash.XXH32.update("bar")
  |> XXHash.XXH32.digest()
  |> Integer.to_string(16)

Currently I don't think this library really supports that and I am having a difficult time understanding how this could be shimmed in without some breaking changes.

Side note, xxh3 was released in v0.7 not too long ago seems interesting https://github.com/Cyan4973/xxHash#new-experimental-hash-algorithm

I'll fork this and see what I can come up with.

[warmwaffles]

My temporary solution to unblock myself was to just append everything I wanted to a string and then call xxh32 on it.

[ttvd]

Hello! I don't have time to do this atm, but I will be more than happy to merge your changes!