add simple coroutine support for promises (based on proposal at Kotlin/kotlinx.coroutines#33)

Author: rivasdiaz

src/main/kotlin/helloworld/Coroutines.kt

@@ -0,0 +1,30 @@
+package helloworld
+
+import kotlin.coroutines.experimental.Continuation
+import kotlin.coroutines.experimental.CoroutineContext
+import kotlin.coroutines.experimental.EmptyCoroutineContext
+import kotlin.coroutines.experimental.startCoroutine
+import kotlin.coroutines.experimental.suspendCoroutine
+import kotlin.js.Promise
+
+fun <T> async(block: suspend () -> T) = Promise<T> { resolve, reject ->
+
+    block.startCoroutine(completion = object : Continuation<T> {
+
+        override val context: CoroutineContext = EmptyCoroutineContext
+
+        override fun resume(value: T) {
+            resolve(value)
+        }
+
+        override fun resumeWithException(exception: Throwable) {
+            reject(exception)
+        }
+    })
+}
+
+fun launch(block: suspend () -> Unit) = async(block)
+
+suspend fun <T> Promise<T>.await(): T = suspendCoroutine {
+    then(it::resume).catch(it::resumeWithException)
+}