Workers draft (#655)

backend.native/tests/runtime/workers/worker0.kt

@@ -0,0 +1,13 @@
+import konan.worker.*
+
+fun main(args: Array<String>) {
+    val worker = startWorker()
+    val future = worker.schedule(TransferMode.CHECKED, { "Input".shallowCopy()}) {
+        input -> input + " processed"
+    }
+    future.consume {
+        result -> println("Got $result")
+    }
+    worker.requestTermination().consume { _ -> }
+    println("OK")
+}