重写脚本解释器的实现，提高其可读性。

Serein.Script/Node/ValueNode/CharNode.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Serein.Script.Node
+{
+    internal class CharNode : ASTNode
+    {
+        public char Value { get; }
+        public CharNode(string value)
+        {
+            Value = char.Parse(value);
+        }
+    }
+}