message: Add typedefs to simplify the callback signature
diff: @@ -37,6 +37,9 @@ namespace adios2
  * Close */
  class Engine
  {
  +public:
  + using AdvanceAsyncCallback =
  + std::function<void(std::shared_ptr<adios2::Engine>)>;
  public:
  /**
  @@ -247,9 +250,8 @@ public:
  * readers
  * @param callback Will be called when advance is completed.
  */
  - virtual void
  - AdvanceAsync(const AdvanceMode mode,
  - std::function<void(std::shared_ptr<adios2::Engine>)> callback);
  + virtual void AdvanceAsync(const AdvanceMode mode,
  + AdvanceAsyncCallback callback);
  AdvanceStatus GetAdvanceStatus();
  