Add fake method that fakes! for the duration of the block

[textgoeshere]

Addresses half of #2

[textgoeshere]

The README says:

Using fake! and fake prevents any events from being broadcast.

but that only applies to events to subscribers that are subscribed after #fake! (or within the #fake block). Global listeners subscribed in an initializer, for example, won't get faked.

What's your view - should #fake! etc. actually fake out existing registrations?

[krisleech]

Good question, my feeling is that #fake! should definitely fake out existing registrations. I'm surprised it doesn't already do this because glancing at the code it looks like every broadcaster is replaced by FakeBroadcaster.

[krisleech]

PR looks good, thanks!