Stop using `Rake` for running benchmarks

This changes the benchmarks to stop using `Rake` and just use
the Sanford CLI and ruby scripts. This minimizes using Rake with
the gem and only requires it for gem building. I'd rather not rely
on extra dependencies that are not needed and for this case, Rake
isn't needed.

This removes the "run X requests against the Benchmark server"
functionality. This hasn't been used since Sanford has been stable
and isn't related to "benchmarking". It was more of a system test
to see that everything worked when running a server.
Merge pull request #132 from redding/jcr-bench-no-rake

Stop using `Rake` for running benchmarks
Rename `FakeConnection` to `FakeServerConnection` and simplify

This renames the test support `FakeConnection` to
`FakeServerConnection` and simplifies it. The goal of this is to
clarify the difference between a fake protocol connection, which
is part of `Sanford::Protocol` and a fake server connection which
is part of `Sanford`. This also simplifies its implementation. It
was previously used for other tests and had extra behavior built
into it. It is now used only for server and worker unit tests so
its behavior could be scaled back.