Added setuptools support, including entrypoints for mitm server and client

Patch for https://github.com/google/nogotofail/issues/10 (setuputils) against `master` since `client_psutil` was merged recently.

Defined version in top package `__init__.py`. Chose `0.1.0` for no particular reason, since it's an upstream decision. Also, some projects define and read version from a top directory `VERSION` file, which i'd prefer since it makes the version top level info and more readable from other non-python tools, but this is a starting point anyway.