Include all 4 sync/async client/server combos

smaller number of threads sending the RPCs. This increases the
likelyhood of race-conditions on receiving threads.

Also make num_threads and num_rpcs as command-line flags

improve code reuse

'TestService' in test.proto

- make the directory structure match the package structure
- sanitize the package structure (test --> testing)
- add auto-detection of proto file dependencies

Pass #2.

appropriate

Rename ThreadPool -> FixedSizeThreadPool to allow for later introduction
of DynamicSizeThreadPool