Consider a different concurrency model for the framework

The framework currently uses "thread-per-connection" concurrency model. This was simple to implement, but may not be what we want as it places no practical limits on the number of threads and connections.

We may want to consider something like a fixed thread-pool. I am partial to the [Leader/Followers Pattern][1] (obviously), but a single thread for I/O and a thread-pool to handle each request could be made to work too.

Only once we have decided on the threading model does it make sense to talk about controlling the thread pool sizes as discussed in #25

[1]: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.35.9475&rep=rep1&type=pdf