This adds another round of improvements to the KGB code, with a goal of

better documenting the operations we perform and improving readability

all throughout.
FunctionSpy.__init__ has been broken up into a few functions. Two of

the major parts, the logic around patching the owner to prevent spy

conflicts and the creation of the proxy function, have been split into

new, documented methods. This makes these parts easier to reason about.
The rest of the function has been slightly reorganized to do as little

as possible before we perform validation of arguments and signatures,

and to group together as much of the state setting as possible.
Comments have been added throughout, to better help understand what's

going on and to encourage the organization of new code.
A lot of variable accesses have been reduced. There are many functions

where we'd repeatedly access the same attributes from the spy over and

over, and this wasn't efficient and added to the visual noise of the

function. We now pull out variables we use over and over.

Unit tests pass on all supported versions of Python.