Introducing kgb, the spy agency for Python unit tests.

kgb provides Jasmine-like spy functionality for Python unit tests. It
makes it very easy to spy on functions, block access to them, reroute to
fake functions, check on calls, and so on.

This is a simple Python module with no dependencies. It's trivial to
use, fully documented, and awesome.

Wrote lots of unit tests for it, which pass.