Fixed String escaping

JSONString.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Text;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace ln.json
 {
@@ -16,6 +18,8 @@ namespace ln.json
 			System.Tuple.Create('t','\t'),
 		};
 
+        static HashSet<char> escapeSet = new HashSet<char>(escapeCharacters.Select((x) => x.Item2));
+
         public string Value { get; private set; }
         public override object ToNative() => Value;
 
@@ -31,11 +35,9 @@ namespace ln.json
         }
 
         public static string Escape(string source){
-			StringBuilder sb = new StringBuilder();
+            StringBuilder sb = new StringBuilder();
 			foreach (char ch in source){
-                if ((ch >= 0x20) && (ch < 128)) {
+                if (escapeSet.Contains(ch)) {
-                    sb.Append(ch);
-                } else if (ch < 0x20) {
                     foreach (System.Tuple<char, char> repl in escapeCharacters) {
                         if (repl.Item2 == ch) {
                             sb.Append("\\");
@@ -43,6 +45,10 @@ namespace ln.json
                             break;
                         }
                     }
+                }
+                else if (ch < 128)
+                {
+                    sb.Append(ch);
                 } else {
                     byte[] bytes = BitConverter.GetBytes((int)ch);
                     sb.Append("\\u");