Introduce Slack chat room.
Fix visibility of RACScheduler+Subclass.h

It should be public for consumers to use, just like RACQueueScheduler+Subclass.h.
Merge pull request #1387 from ReactiveCocoa/fix-scheduler-subclass-visibility

Fix visibility of RACScheduler+Subclass.h
Rephrase note
Merge pull request #1381

Fixes #871.
Point more directly to the "What to do" part for Slack

If you arrive at the top of that issue it's super confusing, link more towards the anchor where people are dropping in Emails
Merge pull request #1388 from paulcbetts/patch-1

Point more directly to the "What to do" part for Slack
Categorize things into neat Xcode groups
Move to specta/specta, specta/expecta, and XCTest
Only build the active architecture to test iOS
Merge pull request #1393 from ReactiveCocoa/xctest

Move to specta/specta, specta/expecta, and XCTest
Merge jspahrsummers/RxSwift@15734da
Update bridging, move into implementation files
Better docs for toSignal
Move Observable.constant definition up a bit
Restore bridging header to improve type safety

fromSignal() is kinda janky and unsafe, so extending RACSignal is a
better idea.
Add Promise.toSignal
Add Action.swift to project and targets
Add Observable.toInfiniteSignal
Add RACSignal.toObservable