Add benchmark

[erikologic]

Hey nice library!

Would be good to understand the perks and what not of using this against an imperative approach.
Can you add benchmarks reports in the README file pls?

[Primetalk]

1. Thanks.
2. There is some overhead caused by wrappers and lazy evaluations. For instance, it's unreasonable to expect good performance sending separate bytes via stream. However, when using with large byte buffers or data structures, the overhead should be negligible.
3. The advantage of the io/stream is in the absence of some classes of bugs, and ability to create complex bug-free programs.
4. Eventually will add. Feel free to create a PR if you need it sooner.