message: Support e=None for bottleneck_distance
diff: #include <pybind11_diagram_utils.h>
  -double bottleneck(Dgm d1, Dgm d2, double epsilon)
  +// For compatibility with older versions, we want to support e=None.
  +// In C++17, the recommended way is std::optional<double>.
  +double bottleneck(Dgm d1, Dgm d2, py::object epsilon)
  {
  + double e = (std::numeric_limits<double>::min)();
  + if (!epsilon.is_none()) e = epsilon.cast<double>();
  // I *think* the call to request() has to be before releasing the GIL.
  auto diag1 = numpy_to_range_of_pairs(d1);
  auto diag2 = numpy_to_range_of_pairs(d2);
  py::gil_scoped_release release;
  - return Gudhi::persistence_diagram::bottleneck_distance(diag1, diag2, epsilon);
  + return Gudhi::persistence_diagram::bottleneck_distance(diag1, diag2, e);
  }
  PYBIND11_MODULE(bottleneck, m) {
  m.attr("__license__") = "GPL v3";
  m.def("bottleneck_distance", &bottleneck,
  py::arg("diagram_1"), py::arg("diagram_2"),
  - py::arg("e") = (std::numeric_limits<double>::min)(),
  + py::arg("e") = py::none(),
  R"pbdoc(
  This function returns the point corresponding to a given vertex.
  