Port tests to pytest

Use simple asserts and pytest's powerful introspection to make testing
simpler. This merges the old .py/.ref file pairs into simple .py files
where the expected values are right next to the code being tested.

This commit does not touch the C++ part of the code and replicates the
Python tests exactly like the old .ref-file-based approach.

tests/test_stl_binders.cpp

@@ -0,0 +1,37 @@
+/*
+    tests/test_stl_binders.cpp -- Usage of stl_binders functions
+
+    Copyright (c) 2016 Sergey Lyskov
+
+    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"
+
+#include <pybind11/stl_bind.h>
+
+class El {
+public:
+	El() = delete;
+	El(int v) : a(v) { }
+
+	int a;
+};
+
+std::ostream & operator<<(std::ostream &s, El const&v) {
+	s << "El{" << v.a << '}';
+	return s;
+}
+
+void init_ex_stl_binder_vector(py::module &m) {
+	py::class_<El>(m, "El")
+		.def(py::init<int>());
+
+	py::bind_vector<unsigned int>(m, "VectorInt");
+	py::bind_vector<bool>(m, "VectorBool");
+
+	py::bind_vector<El>(m, "VectorEl");
+
+    py::bind_vector<std::vector<El>>(m, "VectorVectorEl");
+}