moved the particle system and the entity component system into their own nuget packages

Source/MonoGame.Extended.Particles/Modifiers/VortexModifier.cs

@@ -0,0 +1,29 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Particles.Modifiers
+{
+    public unsafe class VortexModifier : IModifier
+    {
+        // Note: not the real-life one
+        private const float _gravConst = 100000f;
+        public Vector2 Position { get; set; }
+        public float Mass { get; set; }
+        public float MaxSpeed { get; set; }
+
+        public void Update(float elapsedSeconds, ParticleBuffer.ParticleIterator iterator)
+        {
+            while (iterator.HasNext)
+            {
+                var particle = iterator.Next();
+                var diff = Position + particle->TriggerPos - particle->Position;
+
+                var distance2 = diff.LengthSquared();
+
+                var speedGain = _gravConst*Mass/distance2*elapsedSeconds;
+                // normalize distances and multiply by speedGain
+                diff.Normalize();
+                particle->Velocity += diff*speedGain;
+            }
+        }
+    }
+}