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_numpy_vectorize.cpp

@@ -0,0 +1,41 @@
+/*
+    tests/test_numpy_vectorize.cpp -- auto-vectorize functions over NumPy array
+    arguments
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    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/numpy.h>
+
+double my_func(int x, float y, double z) {
+    std::cout << "my_func(x:int=" << x << ", y:float=" << y << ", z:float=" << z << ")" << std::endl;
+    return (float) x*y*z;
+}
+
+std::complex<double> my_func3(std::complex<double> c) {
+    return c * std::complex<double>(2.f);
+}
+
+void init_ex_numpy_vectorize(py::module &m) {
+    // Vectorize all arguments of a function (though non-vector arguments are also allowed)
+    m.def("vectorized_func", py::vectorize(my_func));
+
+    // Vectorize a lambda function with a capture object (e.g. to exclude some arguments from the vectorization)
+    m.def("vectorized_func2",
+        [](py::array_t<int> x, py::array_t<float> y, float z) {
+            return py::vectorize([z](int x, float y) { return my_func(x, y, z); })(x, y);
+        }
+    );
+
+    // Vectorize a complex-valued function
+    m.def("vectorized_func3", py::vectorize(my_func3));
+
+    /// Numpy function which only accepts specific data types
+    m.def("selective_func", [](py::array_t<int, py::array::c_style>) { std::cout << "Int branch taken." << std::endl; });
+    m.def("selective_func", [](py::array_t<float, py::array::c_style>) { std::cout << "Float branch taken." << std::endl; });
+    m.def("selective_func", [](py::array_t<std::complex<float>, py::array::c_style>) { std::cout << "Complex float branch taken." << std::endl; });
+}