重写脚本解释器的实现，提高其可读性。

Serein.Script/Node/FlowControl/IfNode.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Serein.Script.Node.FlowControl
+{
+    /// <summary>
+    /// 条件节点
+    /// </summary>
+    public class IfNode : ASTNode
+    {
+        /// <summary>
+        /// 条件来源
+        /// </summary>
+        public ASTNode Condition { get; }
+
+        /// <summary>
+        /// 条件为 true 时所执行的语句
+        /// </summary>
+        public List<ASTNode> TrueBranch { get; }
+
+        /// <summary>
+        /// 条件为 false 时所执行的语句
+        /// </summary>
+        public List<ASTNode> FalseBranch { get; }
+        public IfNode(ASTNode condition, List<ASTNode> trueBranch, List<ASTNode> falseBranch)
+            => (Condition, TrueBranch, FalseBranch) = (condition, trueBranch, falseBranch);
+    }
+
+}