feat(color): Add Darker and Lighter Function

Author: Alexis Huvier

SharpEngine/Utils/Color.cs

@@ -78,6 +78,20 @@ public Color(int r, int g, int b, int a)
         A = a;
     }
 
+    /// <summary>
+    /// Return Darker Color
+    /// </summary>
+    /// <param name="force">Force of Darker Color</param>
+    /// <returns>Darker Color</returns>
+    public Color Darker(int force = 1) => new(_r - 10 * force, _g - 10 * force, _b - 10 * force, _a);
+
+    /// <summary>
+    /// Return Lighter Color
+    /// </summary>
+    /// <param name="force">Force of Lighter Color</param>
+    /// <returns>Lighter Color</returns>
+    public Color Lighter(int force = 1) => new(_r + 10 * force, _g + 10 * force, _b + 10 * force, _a);
+
     /// <summary>
     /// Transition Color to target color
     /// </summary>