Add -[RACSignal deliverOnMainThread]
Merge pull request #1577 from ReactiveCocoa/cartfile

Use Carthage for submodule management
Refactor KVO code to use weak references

Whenever possible, annotate public parameters as such too, so the
compiler will error if it knows a weak reference can’t be formed to a
particular class.
Simplify -rac_valuesAndChangesForKeyPath:
Tear down KVO with an unsafe reference

A weak reference won’t live long enough for us to do so.
Allow nil observers in rac_valuesAndChanges…
Only invoke -rac_valuesForKeyPath: against `id`

Addresses
https://github.com/ReactiveCocoa/ReactiveCocoa/pull/1595#discussion_r212
00958.
wow observer, you're so strong
Merge pull request #1595 from ReactiveCocoa/weak-references

Use weak references in KVO observation
Cherry picked from aborted 3.0 - Replace -didSubscribe…: with a disposable property
Charry picked from aborted 3.0 - 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.
Remove mention of Slack chat room

It's not valuable for most users, being primarily used for conversations between collaborators.

See https://github.com/ReactiveCocoa/ReactiveCocoa/issues/871#issuecomment-66137012.
Undo changes made to the project file by Xcode - should get folded into 076d38e.
Merge pull request #1604 from ReactiveCocoa/jspahrsummers-patch-1

Remove mention of Slack chat room
Queue events and drain them on the main thread.
Merge branch 'master' into deliver-to-ui
Make delivery code more similar to RACSubscriber.
Remove unnecessary nil check.
Revert to delivering one event per run loop.

This reverts commits 97da8702ebbfc6f869ca4a20b255a6825d31cc23, 07c927e976eaf7df76a2c73947d534ebcc8e7d12, ade0a6310bb86121a3142527f54cd74169ec0958.
Merge pull request #1597 from talko/backportlivesubscriber

Backport RACLiveSubscriber from aborted 3.0 branch.