Support merging plugins into winsw.exe executable

* Decouple Core components into WinSWCore projects.
* Use ILMerge to merge everything (inc. Plugins) into a single executable

TODO: API Should be refactored before the publishing
TODO: check signing procedure

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>

Conflicts:
	src/Core/ServiceWrapper/winsw.csproj

Conflicts:
	src/Core/ServiceWrapper/Main.cs
	src/winsw.sln

src/Core/WinSWCore/Download.cs

@@ -0,0 +1,48 @@
+using System;
+using System.IO;
+using System.Net;
+using System.Xml;
+
+namespace winsw
+{
+    /// <summary>
+    /// Specify the download activities prior to the launch.
+    /// This enables self-updating services.
+    /// </summary>
+    public class Download
+    {
+        public readonly string From;
+        public readonly string To;
+
+        internal Download(XmlNode n)
+        {
+            From = Environment.ExpandEnvironmentVariables(n.Attributes["from"].Value);
+            To = Environment.ExpandEnvironmentVariables(n.Attributes["to"].Value);
+        }
+
+        public void Perform()
+        {
+            WebRequest req = WebRequest.Create(From);
+            WebResponse rsp = req.GetResponse();
+            FileStream tmpstream = new FileStream(To + ".tmp", FileMode.Create);
+            CopyStream(rsp.GetResponseStream(), tmpstream);
+            // only after we successfully downloaded a file, overwrite the existing one
+            if (File.Exists(To))
+                File.Delete(To);
+            File.Move(To + ".tmp", To);
+        }
+
+        private static void CopyStream(Stream i, Stream o)
+        {
+            byte[] buf = new byte[8192];
+            while (true)
+            {
+                int len = i.Read(buf, 0, buf.Length);
+                if (len <= 0) break;
+                o.Write(buf, 0, len);
+            }
+            i.Close();
+            o.Close();
+        }
+    }
+}