added benches

[makoConstruct]

resolves #2

[vadixidav]

@makoConstruct Two things:

1. Take care of the issues CI identified, it should be fairly simple
2. If you know how to, or can figure it out, please add a GitHub Action to add the benchmarks to CI (cargo bench) using the existing template already there

If you are done with this or want me to do either of these things, just let me know and I will follow up when I have time.

[makoConstruct]

oops, that's not even being used. I brought it in to do Vec's thing of starting with an allocation of a sensible initial capacity, but realized it doesn't really translate directly to us, because the allocation has to include the header, and I'm not sure how to calculate that. (I'll think about it)

[vadixidav]

I am going to merge this. The documentation, benchmarks, etc are helpful. If you have additional performance tweaks, please open those as new PRs.