WIP implementation of FutureStream.

tests/async/tfuturestream.nim

@@ -0,0 +1,19 @@
+import asyncdispatch
+
+var fs = newFutureStream[string]()
+
+proc alpha() {.async.} =
+  for i in 0 .. 5:
+    fs.put($i)
+    await sleepAsync(1000)
+
+  fs.complete()
+
+proc beta() {.async.} =
+  while not fs.finished():
+    echo(await fs.takeAsync())
+
+  echo("Finished")
+
+asyncCheck alpha()
+asyncCheck beta()