Hardcopy of pybind11 instead of using git submodules (#552)

* removed pybind as submodule
* added hardcopy of pybind11 2.10.0
* rename pybind11 folder to avoid conflicts when changing branch

Co-authored-by: Dhanya Thattil <dhanya.thattil@psi.ch>

libs/pybind/tests/test_union.cpp

@@ -0,0 +1,22 @@
+/*
+    tests/test_class.cpp -- test py::class_ definitions and basic functionality
+
+    Copyright (c) 2019 Roland Dreier <roland.dreier@gmail.com>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include "pybind11_tests.h"
+
+TEST_SUBMODULE(union_, m) {
+    union TestUnion {
+        int value_int;
+        unsigned value_uint;
+    };
+
+    py::class_<TestUnion>(m, "TestUnion")
+        .def(py::init<>())
+        .def_readonly("as_int", &TestUnion::value_int)
+        .def_readwrite("as_uint", &TestUnion::value_uint);
+}