Added missing concrete poster engines

prs.shared/Posters/MYOB/BillMYOBPoster.cs

@@ -237,3 +237,4 @@ public class BillMYOBPoster : IMYOBPoster<Bill, BillMYOBPosterSettings>
         return results;
     }
 }
+public class BillMYOBPosterEngine<T> : MYOBPosterEngine<Bill, BillMYOBPosterSettings> { }

prs.shared/Posters/MYOB/ReceiptMYOBPoster.cs

@@ -174,3 +174,5 @@ public class ReceiptMYOBPoster : IMYOBPoster<Receipt, ReceiptMYOBPosterSettings>
         return results;
     }
 }
+
+public class ReceiptMYOBPosterEngine<T> : MYOBPosterEngine<Receipt, ReceiptMYOBPosterSettings> { }

prs.shared/Posters/MYOB/SupplierMYOBPoster.cs

@@ -238,3 +238,4 @@ public class SupplierMYOBPoster : IMYOBPoster<Supplier, SupplierMYOBPosterSettin
         return results;
     }
 }
+public class SupplierMYOBPosterEngine<T> : MYOBPosterEngine<Supplier, SupplierMYOBPosterSettings> { }