Benchmark and README

@sam-github Please review.

- I reworked the benchmark to support more scenarios and also fork a new process for the server (to have one process for benchmark client and another for cluster master).
- I have also extracted out the server, so that we can run it on its own for testing session reuse with different clients too (e.g. `openssl s_client`)

And finally I have modified README, removed all mentions of benchmarks and added an advice that users should measure the performance in their specific scenario to decide how much performance can be gained.