Add a 3.0 heading to the changelog
Mark all 2.0 deprecations as unavailable instead

Stop maintaining their implementations. Everyone should have migrated
by the time they're on 3.0.
Add RACDeprecated macro to mark 3.0 deprecations

Consumers can define WE_PROMISE_TO_MIGRATE_TO_REACTIVECOCOA_3_0 to
squelch these warnings/errors.
Deprecate RACBehaviorSubject, test RACDeprecated
Allow nil for -addDisposable:
Remove nil checks before invoking -addDisposable:
Merge pull request #879 from ReactiveCocoa/add-nil-disposable

Allow nil for -[RACCompoundDisposable addDisposable:]
Merge remote-tracking branch 'origin/master' into 3.0-development
Merge branch '3.0-development' into deprecations
Merge branch 'deprecations' into signal-provider

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa.xcodeproj/project.pbxproj