Added simplest possible test example.

example/lambert_w_basic_example.cpp

@@ -0,0 +1,20 @@
+// Copyright Paul A. Bristow 2018
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/math/special_functions/lambert_w.hpp> // For lambert_w0 and wm1 functions.
+
+//#include <iostream>
+//#include <iomanip>
+
+int main()
+{
+ double z = 2.0;
+ double w = boost::math::lambert_w0(z);
+  std::cout.setf(std::ios_base::showpoint); // Include any trailing zeros.
+  std::cout.precision(std::numeric_limits<double>::max_digits10); // Show all possibly significant digits.
+  std::cout << " lambert_w0(" << z << ") = " << w << std::endl;
+  return 0;
+} // int main()