add preliminary support for merits gained

EDPlayerJournal/BGS/Parsers/PowerplayParser.cs

@@ -0,0 +1,29 @@
+using EDPlayerJournal.Entries;
+
+namespace EDPlayerJournal.BGS.Parsers;
+
+internal class PowerplayParser : ITransactionParserPart {
+    public void Parse(Entry entry, TransactionParserContext context, TransactionParserOptions options, TransactionList transactions) {
+        PowerplayEntry? p = entry as PowerplayEntry;
+        if (p == null) {
+            return;
+        }
+
+        if (context.LastMerits == null) {
+            context.LastMerits = p.Merits;
+        }
+
+        context.CurrentMerits = p.Merits;
+ 
+        if (context.LastMerits != context.CurrentMerits) {
+            transactions.Add(new MeritsGained(entry) {
+                Merits = ((long)(context.CurrentMerits - context.LastMerits)),
+                Power = p.Power,
+                System = context.CurrentSystem,
+                Faction = p.Power,
+            });
+        }
+
+        context.LastMerits = context.CurrentMerits;
+    }
+}