修复一些错误并更新README

ExpressionElements/MemberElements/Indexer.cs

@@ -9,7 +9,9 @@ using Flee.PublicTypes;
 
 namespace Flee.ExpressionElements.MemberElements
 {
-    [Obsolete("Element representing an array index")]
+    /// <summary>
+    /// 表示数组索引的表达式元素
+    /// </summary>
     internal class IndexerElement : MemberElement
     {
         private ExpressionElement _myIndexerElement;