(doc) Documented the internal design of Hyper.

This includes a rationale and description of the overall design of Hyper as
well as providing a guide to understanding and navigating the source.

This also updates and adds new benchmarks for the Server and mocking the Clients.
I'd rather there not be an example in the README, as it can bitrot as the library is still unstable.

How about a link to the example source file.