THRIFT-4478: Thrift will not build with dlang 2.078 or later (#1559)

* THRIFT-4478 Thrift will not build with dlang 2.078 or later

This fixes build errors and deprecation warnings on dmd v2.080.0.

* THRIFT-4478: Update ubuntu-artful docker build image to use DMD 2.080.0

* THRIFT-4478 Fix build failure for nonblocking

* THRIFT-4478: update readme files
diff --git a/lib/d/test/client_pool_test.d b/lib/d/test/client_pool_test.d
index 85bcb29..52207d9 100644
--- a/lib/d/test/client_pool_test.d
+++ b/lib/d/test/client_pool_test.d
@@ -409,8 +409,8 @@
     )();
     Thread.sleep(dur!"msecs"(20));
     auto resultTuple = partialResult.finishGet();
-    enforce(resultTuple._0 == ports[0 .. 2]);
-    enforce(equal(map!"a.port"(cast(TestServiceException[])resultTuple._1),
+    enforce(resultTuple[0] == ports[0 .. 2]);
+    enforce(equal(map!"a.port"(cast(TestServiceException[])resultTuple[1]),
       ports[3 .. $ - 1]));
   }
 }