Add support for magic methods

[jsatt]

Magic methods in Python are set differently then normal attributes, making them difficult to mock out. This would allow Fake instances to be used as context managers.

[kumar303]

I once looked at how hard it would be to make mock the backend for fudge. It's very doable. This would make a lot of sense since mock is part of the stdlib now. There was one patch that fudge needed (I forget what it is) but it was merged into mock a long time ago. It would greatly simplify all of fudge's patching code and fix a lot of bugs since it isn't as robust as mock's.

[jsatt]

@kumar303, I've long been considering a fudge-like library to abstract a lot Mock's interface (even before we contacted you about working on fudge) and had planned to get your thoughts on making a fudge 2.0 or separate project to make that happen.

This was just a pain point I was banging my head against for a while today before I realized the problem, and I think it could be fixed in fudge's current state (but way easier with a Mock backend). I found a work around that I'm still fleshing out and I may bang on this once I'm clear on the right generic solution.