Include startCoroutineCancellable into docs

Author: elizarov

kotlinx-coroutines-core/src/main/kotlin/kotlinx/coroutines/experimental/Cancellable.kt

@@ -22,17 +22,13 @@ import kotlin.coroutines.experimental.intrinsics.createCoroutineUnchecked
 /**
  * Use this function to start coroutine in a cancellable way, so that it can be cancelled
  * while waiting to be dispatched.
- *
- * @suppress **This is unstable API and it is subject to change.**
  */
 internal fun <T> (suspend () -> T).startCoroutineCancellable(completion: Continuation<T>) =
     createCoroutineUnchecked(completion).resumeCancellable(Unit)
 
 /**
  * Use this function to start coroutine in a cancellable way, so that it can be cancelled
  * while waiting to be dispatched.
- *
- * @suppress **This is unstable API and it is subject to change.**
  */
 internal fun <R, T> (suspend (R) -> T).startCoroutineCancellable(receiver: R, completion: Continuation<T>) =
     createCoroutineUnchecked(receiver, completion).resumeCancellable(Unit)