feat: add basic support for SVG generator.

Add heat map example.

samples/HeatMap/Utils/UtilsExtensions.cs

@@ -0,0 +1,25 @@
+namespace HotMap.Utils;
+
+public static class UtilsExtensions
+{
+    extension(DateOnly date)
+    {
+        public DateOnly GetMonday()
+        {
+            return date.DayOfWeek switch
+            {
+                DayOfWeek.Monday => date,
+                DayOfWeek.Sunday => date.AddDays(-6),
+                _ => date.AddDays(1 - (int)date.DayOfWeek)
+            };
+        }
+    }
+
+    extension<T>(IEnumerable<T> enumerable)
+    {
+        public IEnumerable<(T, int)> WithIndex()
+        {
+            return enumerable.Select((v, i) => (v, i));
+        }
+    }
+}