feat: Add Absolute Price Oscillator (APO) implementation and documentation

feat: Implement ADL (Accumulation/Distribution Line) indicator

lib/volume/adl/Adl.Quantower.cs

@@ -0,0 +1,43 @@
+using System.Drawing;
+using TradingPlatform.BusinessLayer;
+
+namespace QuanTAlib;
+
+public class AdlIndicator : Indicator, IWatchlistIndicator
+{
+    private Adl? _adl;
+    protected LineSeries? AdlSeries;
+
+    public static int MinHistoryDepths => 0;
+    int IWatchlistIndicator.MinHistoryDepths => MinHistoryDepths;
+
+    public override string ShortName => "ADL";
+    public override string SourceCodeLink => "https://github.com/mihakralj/QuanTAlib/blob/main/lib/volume/adl/Adl.Quantower.cs";
+
+    public AdlIndicator()
+    {
+        OnBackGround = true;
+        SeparateWindow = true;
+        Name = "ADL - Accumulation/Distribution Line";
+        Description = "Accumulation/Distribution Line";
+
+        AdlSeries = new(name: "ADL", color: Color.Blue, width: 2, style: LineStyle.Solid);
+        AddLineSeries(AdlSeries);
+    }
+
+    protected override void OnInit()
+    {
+        _adl = new Adl();
+        base.OnInit();
+    }
+
+    protected override void OnUpdate(UpdateArgs args)
+    {
+        bool isNew = args.Reason == UpdateReason.NewBar || args.Reason == UpdateReason.HistoricalBar;
+
+        TBar bar = this.GetInputBar(args);
+        TValue result = _adl!.Update(bar, isNew);
+
+        AdlSeries!.SetValue(result.Value);
+    }
+}