新增verlet物理引擎（实验性）

source/src/Physics/Verlet/Composites/LineSegments.ts

@@ -0,0 +1,20 @@
+module es {
+    export class LineSegments extends Composite {
+        constructor(vertices: Vector2[], stiffness: number) {
+            super();
+
+            for (let i = 0; i < vertices.length; i ++) {
+                const p = new Particle(vertices[i]);
+                this.addParticle(p);
+
+                if (i > 0)
+                    this.addConstraint(new DistanceConstraint(this.particles[i], this.particles[i - 1], stiffness));
+            }
+        }
+
+        public pinParticleAtIndex(index: number): LineSegments {
+            this.particles[index].pin();
+            return this;
+        }
+    }
+}