message: Adding ImprovedSamplingDecorator to plugin system
diff: #include "CircuitOptimizer.hpp"
  #include "ROErrorDecorator.hpp"
  +#include "ImprovedSamplingDecorator.hpp"
  #include <memory>
  #include <set>
  @@ -69,6 +70,7 @@ public:
  auto opt = std::make_shared<xacc::quantum::CircuitOptimizer>();
  auto roed = std::make_shared<xacc::quantum::ROErrorDecorator>();
  + auto impsamplingd = std::make_shared<xacc::quantum::ImprovedSamplingDecorator>();
  context.RegisterService<xacc::IRProvider>(giservice);
  context.RegisterService<xacc::Preprocessor>(kp);
  @@ -84,6 +86,9 @@ public:
  context.RegisterService<xacc::AcceleratorDecorator>(roed);
  context.RegisterService<xacc::Accelerator>(roed);
  + context.RegisterService<xacc::AcceleratorDecorator>(impsamplingd);
  + context.RegisterService<xacc::Accelerator>(impsamplingd);
  +
  auto h = std::make_shared<xacc::quantum::Hadamard>();
  auto cn = std::make_shared<xacc::quantum::CNOT>();
  auto cp = std::make_shared<xacc::quantum::CPhase>();
  