kraken: engine: add 'CsvEngineListern.output'

Otherwise it would be difficult to actually get access to the output...

src/engine/csv-engine-listener.cc

@@ -6,6 +6,10 @@ CsvEngineListener::CsvEngineListener() = default;
 
 CsvEngineListener::~CsvEngineListener() = default;
 
+csv::csv_type const& CsvEngineListener::output() const {
+    return output_;
+}
+
 void CsvEngineListener::on_acknowledgement(User user, UserOrderId id) {
     output_.emplace_back(csv::csv_line_type{
         "A",

src/engine/csv-engine-listener.hh

@@ -13,6 +13,8 @@ struct CsvEngineListener : EngineListener {
 
     virtual ~CsvEngineListener();
 
+    csv::csv_type const& output() const;
+
     /// Called when a new trade or cancel order has been acknowledged.
     void on_acknowledgement(User user, UserOrderId id) override;