Replace -didSubscribe…: with a disposable property
Skip adding disposables that are already disposed
Replace uses of +createSignal: with +create:
Merge branch 'deprecate-sequences' into subscriber-disposal

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/RACSignal+Operations.m
Merge branch 'deprecate-sequences' into subscriber-disposal
Add RACLiveSubscriber, reduce subscriber allocations

Since RACLiveSubscriber fulfills the use cases of _both_ RACSubscriber
and RACPassthroughSubscriber, we can avoid creating _two_ subscribers
for every block-based subscription, and just reuse the same object
instead.
Refactor -bind: for early termination of synchronous signals
Add -subscribeSavingDisposable:next:error:completed:
Refactor -bind: to use -subscribeSavingDisposable:…
Merge remote-tracking branch 'origin/3.0-development' into subscriber-disposal
Merge remote-tracking branch 'origin/3.0-development' into subscriber-disposal
Fix indentation in NSString+RACSupport
Merge branch '3.0-development' into subscriber-disposal
Remove subscription scheduler
Refactor -retry: and -repeat to honor early disposal
Test error handling with -repeat
Tests for -retry:
Test -subscribeSavingDisposable:
Test implicit disposal of other subscriptions in +create:
Update +create: documentation