整理代码结构，支持Package Manager添加

Demo/Runtime/Demo12_CustomDrawing.cs

@@ -0,0 +1,39 @@
+/******************************************/
+/*                                        */
+/*     Copyright (c) 2018 monitor1394     */
+/*     https://github.com/monitor1394     */
+/*                                        */
+/******************************************/
+
+using UnityEngine;
+using UnityEngine.UI;
+
+
+namespace XCharts
+{
+    [DisallowMultipleComponent]
+    [ExecuteInEditMode]
+    public class Demo12_CustomDrawing : MonoBehaviour
+    {
+        LineChart chart;
+        void Awake()
+        {
+            chart = gameObject.GetComponent<LineChart>();
+            if (chart == null) return;
+
+            chart.customDrawCallback = delegate (VertexHelper vh)
+            {
+                var dataPoints = chart.series.list[0].dataPoints;
+                if (dataPoints.Count > 0)
+                {
+                    var pos = dataPoints[3];
+                    var zeroPos = new Vector3(chart.coordinateX, chart.coordinateY);
+                    var startPos = new Vector3(pos.x, zeroPos.y);
+                    var endPos = new Vector3(pos.x, zeroPos.y + chart.coordinateHeight);
+                    ChartDrawer.DrawLine(vh, startPos, endPos, 1, Color.blue);
+                    ChartDrawer.DrawCricle(vh, pos, 5, Color.blue);
+                }
+            };
+        }
+    }
+}