增加代码API注释文档，整理代码

Scripts/UI/Component/Pie.cs

@@ -0,0 +1,38 @@
+using UnityEngine;
+
+namespace XCharts
+{
+    /// <summary>
+    /// the global setting of pie chart.
+    /// 饼图的全局设置。
+    /// </summary>
+    [System.Serializable]
+    public class Pie
+    {
+        [SerializeField] private float m_TooltipExtraRadius;
+        [SerializeField] private float m_SelectedOffset;
+        /// <summary>
+        /// the extra dadius of pie chart when the tooltip indicatored pie.
+        /// 提示框指示时的额外半径。
+        /// </summary>
+        public float tooltipExtraRadius { get { return m_TooltipExtraRadius; } set { m_TooltipExtraRadius = value; } }
+        /// <summary>
+        /// the offset of pie when the pie item is selected.
+        /// 饼图项被选中时的偏移。
+        /// </summary>
+        public float selectedOffset { get { return m_SelectedOffset; } set { m_SelectedOffset = value; } }
+
+        public static Pie defaultPie
+        {
+            get
+            {
+                var pie = new Pie
+                {
+                    m_TooltipExtraRadius = 10f,
+                    m_SelectedOffset = 10f,
+                };
+                return pie;
+            }
+        }
+    }
+}