Coroutine context propagation for Reactor to coroutines API migration (#1377)

* Propagation of the coroutine context of await calls into
  Mono/Flux builder
* Publisher.asFlow propagates coroutine context from `collect`
  call to the Publisher
* Flow.asFlux transform
* Optimized FlowSubscription
* kotlinx.coroutines.reactor.flow package is replaced with kotlinx.coroutines.reactor

Fixes #284
diff --git a/reactive/kotlinx-coroutines-rx2/src/RxConvert.kt b/reactive/kotlinx-coroutines-rx2/src/RxConvert.kt
index d5678de..4b12127 100644
--- a/reactive/kotlinx-coroutines-rx2/src/RxConvert.kt
+++ b/reactive/kotlinx-coroutines-rx2/src/RxConvert.kt
@@ -8,8 +8,7 @@
 import kotlinx.coroutines.*
 import kotlinx.coroutines.channels.*
 import kotlinx.coroutines.flow.*
-import kotlinx.coroutines.reactive.flow.*
-import org.reactivestreams.*
+import kotlinx.coroutines.reactive.*
 import kotlin.coroutines.*
 
 /**
@@ -82,7 +81,7 @@
 
 /**
  * Converts the given flow to a cold observable.
- * The original flow is cancelled if the observable subscriber was disposed.
+ * The original flow is cancelled when the observable subscriber is disposed.
  */
 @JvmName("from")
 @ExperimentalCoroutinesApi
@@ -106,8 +105,8 @@
 }
 
 /**
- * Converts the given flow to a cold observable.
- * The original flow is cancelled if the flowable subscriber was disposed.
+ * Converts the given flow to a cold flowable.
+ * The original flow is cancelled when the flowable subscriber is disposed.
  */
 @JvmName("from")
 @ExperimentalCoroutinesApi