Migrate update system to XML manifest and improve multi-OS support

AlwaysUpToDate/UpdateInfo.cs

@@ -1,14 +1,54 @@
-using System;
-using System.Collections.Generic;
-using System.Text;
+using System.Collections.Generic;
+using System.Xml.Serialization;
 
 namespace AlwaysUpToDate
 {
-    internal class UpdateInfo
+    [XmlRoot("updates")]
+    public class UpdateManifest
     {
+        [XmlElement("item")]
+        public List<UpdateItem> Items { get; set; } = new List<UpdateItem>();
+    }
+
+    public class UpdateItem
+    {
+        [XmlElement("os")]
+        public TargetOS OS { get; set; }
+
+        [XmlElement("version")]
         public string Version { get; set; }
-        public string FileUrl { get; set; }
-        public string AdditionalInformation { get; set; }
-        public bool Mandatory { get; set; }
+
+        [XmlElement("url")]
+        public string DownloadUrl { get; set; }
+
+        [XmlElement("changelog")]
+        public string ChangelogUrl { get; set; }
+
+        [XmlElement("mandatory")]
+        public bool IsMandatory { get; set; }
+
+        [XmlElement("checksum")]
+        public Checksum Checksum { get; set; }
+    }
+
+    public class Checksum
+    {
+        [XmlAttribute("algorithm")]
+        public string Algorithm { get; set; }
+
+        [XmlText]
+        public string Value { get; set; }
+    }
+
+    public enum TargetOS
+    {
+        [XmlEnum("windows")]
+        Windows,
+
+        [XmlEnum("macos")]
+        MacOS,
+
+        [XmlEnum("linux")]
+        Linux,
     }
 }