The config dict is passed alongside the class that the fixture will
eventually initialize. It can use the config dict for optional
arguments to the implementation's constructor.

When I started this feature, I expected passing the "tee" flag
to "syscap" would copy output directly to the calling terminal, to the
original ORIGINAL sys.stdout/sys.stderr. That's not how it works-
it passes output to whatever capture was set earlier! This actually
makes the feature more flexible because it enables tee-like behavior as
well as pytests reporting behavior. Awesome!