message: Fixed QAOA example
diff: int main(int argc, char **argv) {
  xacc::Initialize(argc, argv);
  - // Use the Qpp simulator as the accelerator
  - auto acc = xacc::getAccelerator("qpp");
  - const size_t nbNodes = 8;
  + //xacc::set_verbose(true);
  + //xacc::logToFile(true);
  + //xacc::setLoggingLevel(2);
  +
  + //auto acc = xacc::getAccelerator("qpp");
  + auto acc = xacc::getAccelerator("tnqvm",{
  + std::make_pair("tnqvm-visitor", "exatn:float"),
  + std::make_pair("exatn-buffer-size-gb", 6)
  + });
  + const size_t nbNodes = 24;
  const int nbSteps = 1;
  auto buffer = xacc::qalloc(nbNodes);
  - auto optimizer = xacc::getOptimizer("nlopt");
  + auto optimizer = xacc::getOptimizer("nlopt",{{"nlopt-maxeval",1}});
  auto qaoa = xacc::getService<xacc::Algorithm>("QAOA");
  auto graph = xacc::getService<xacc::Graph>("boost-digraph")->gen_random_graph(nbNodes, 3.0 / nbNodes);
  - const bool initOk =
  - qaoa->initialize({std::make_pair("accelerator", acc),
  + const bool initOk = qaoa->initialize({std::make_pair("accelerator", acc),
  std::make_pair("optimizer", optimizer),
  std::make_pair("graph", graph),
  // number of time steps (p) param
  std::make_pair("steps", nbSteps),
  // "Standard" or "Extended"
  - std::make_pair("parameter-scheme", "Standard")});
  + std::make_pair("parameter-scheme", "Standard")
  + });
  qaoa->execute(buffer);
  std::cout << "Min Val: " << (*buffer)["opt-val"].as<double>() << "\n";
  +
  + xacc::Finalize();
  + return 0;
  }
  