CI fixes (#1744)

* Fix warning that not including a cmake source or build dir will be a fatal error (it is now on newest CMakes)
    * Fixes appveyor
* Travis uses CMake 3.9 for more than a year now
* Travis dropped sudo: false in December
* Dropping Sphinx 2
- clang7: Suppress self-assign warnings; fix missing virtual dtors
- pypy:
  - Keep old version (newer stuff breaks)
  - Pin packages to extra index for speed
- travis:
  - Make docker explicit; remove docker if not needed
  - Make commands more verbose (for debugging / repro)
  - Make Ubuntu dist explicit per job
- Fix Windows
- Add names to travis

tests/test_kwargs_and_defaults.cpp

@@ -34,7 +34,9 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     m.def("kw_func_udl_z", kw_func, "x"_a, "y"_a=0);
 
     // test_args_and_kwargs
-    m.def("args_function", [](py::args args) -> py::tuple { return args; });
+    m.def("args_function", [](py::args args) -> py::tuple {
+        return std::move(args);
+    });
     m.def("args_kwargs_function", [](py::args args, py::kwargs kwargs) {
         return py::make_tuple(args, kwargs);
     });