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.

0.4-beta: for Kotlin 1.1.0-beta-18

• Switched to Kotlin version 1.1.0-beta-18 (republished version).
• CoroutineDispatcher methods now have context parameter.
• Introduced CancellableContinuation.isCancelled
• Introduced EventLoop dispatcher and made it a default for runBlocking { ... }
• Introduced CoroutineScope interface with isActive and context properties;
  standard coroutine builders include it as receiver for convenience.
• Introduced Executor.toCoroutineDispatcher() extension.
• Delay scheduler thread is not daemon anymore, but times out automatically.
• Debugging facilities in newCoroutineContext can be explicitly disabled with -Dkotlinx.coroutines.debug=off.
• xxx-test files are renamed to xxx-example for clarity.
• Fixed NPE in Job implementation when starting coroutine with already cancelled parent job.
• Support cancellation in kotlinx-coroutines-nio module

0.3-beta: for Kotlin 1.1.0-beta-17

Fixed exception unwrapping in fast-path of CompletableFuture.await()