Add blend modes to renderer.

TestGame/TestGame.cs

@@ -74,6 +74,8 @@ public class TestGame : Game
 
     private void DrawEmitter(ParticleEmitter emitter)
     {
+        Renderer.BeginBlended(Voile.Rendering.BlendMode.BlendAdd);
+
         for (int i = 0; i < emitter.Particles.Length; i++)
         {
             var particle = emitter.Particles[i];
@@ -83,6 +85,8 @@ public class TestGame : Game
             Renderer.SetTransform(emitter.OriginPosition + particle.Position, Vector2.Zero);
             Renderer.DrawCircle(16f * particle.Scale, color);
         }
+
+        Renderer.EndBlended();
     }
 
     private ParticleSystem? _particleSystem;