Improve some indicator stuff

Make ROCP computation a little easier to follow
Return the raw type of 'second' in .Of extension

Indicators/IndicatorExtensions.cs

@@ -44,8 +44,9 @@ public static void Update(this IndicatorBase<IndicatorDataPoint> indicator, Date
         /// <param name="first">The indicator that sends data via DataConsolidated even to the second</param>
         /// <param name="waitForFirstToReady">True to only send updates to the second if first.IsReady returns true, false to alway send updates to second</param>
         /// <returns>The reference to the second indicator to allow for method chaining</returns>
-        public static IndicatorBase<IndicatorDataPoint> Of<T>(this IndicatorBase<IndicatorDataPoint> second, IndicatorBase<T> first, bool waitForFirstToReady = true)
+        public static TSecond Of<T, TSecond>(this TSecond second, IndicatorBase<T> first, bool waitForFirstToReady = true)
             where T : BaseData
+            where TSecond : IndicatorBase<IndicatorDataPoint>
         {
             first.Updated += (sender, consolidated) =>
             {

Indicators/RateOfChangePercent.cs

@@ -48,13 +48,15 @@ public RateOfChangePercent(string name, int period)
         /// <returns>A new value for this indicator</returns>
         protected override decimal ComputeNextValue(IReadOnlyWindow<IndicatorDataPoint> window, IndicatorDataPoint input)
         {
-            if (!window.IsReady)
+            // if we're not ready just grab the first input point in the window
+            decimal denominator = !window.IsReady ? window[window.Count - 1] : window.MostRecentlyRemoved;
+
+            if (denominator == 0)
             {
-                // keep returning the delta from the first item put in there to init
-                return window[window.Count - 1] == 0 ? 0 : 100 * (input - window[window.Count - 1]) / window[window.Count - 1];
+                return 0;
             }
 
-            return window.MostRecentlyRemoved == 0 ? 0 : 100 * (input - window.MostRecentlyRemoved) / window.MostRecentlyRemoved;
+            return 100*(input - denominator)/denominator;
         }
     }
 }