0.5-beta: for Kotlin 1.1.0-beta-22

• Switched to Kotlin version 1.1.0-beta-22 (republished version).
• Removed currentCoroutineContext and related thread-locals without replacement.
  Explicitly pass coroutine context around if needed.
• lazyDefer(context) {...} coroutine builder and LazyDeferred interface are introduced.
• The default behaviour of all coroutine dispatchers is changed to always schedule execution of new coroutine
  for later in this thread or thread pool. Correspondingly, CoroutineDispatcher.isDispatchNeeded function
  has a default implementation that returns true.
• NonCancellable context is introduced.
• Performance optimizations for cancellable continuations (fewer objects created).
• A guide on coroutines is added.