Added C# signature example

examples/signature.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace ImgProxy.Examples
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            const string Key = "943b421c9eb07c830af81030552c86009268de4e532ba2ee2eab8247c6da0881";
+            const string Salt = "520f986b998545b4785e0defbc4f3c1203f22de2374a3d53cb7a7fe9fea309c5";
+            const string Url = "http://img.example.com/pretty/image.jpg";
+
+            const string Resize = "fill";
+            const int Width = 300;
+            const int Height = 300;
+            const string Gravity = "no";
+            const int Enlarge = 1;
+            const string Extension = "png";
+
+            var url = GenerateUrl(Key, Salt, Url, Resize, Width, Height, Gravity, Enlarge, Extension);
+
+            Console.WriteLine(url);
+        }
+
+        static string GenerateUrl(string key, string salt, string url, string resize, int width, int height, string gravity, int enlarge, string extension)
+        {
+            var keybin = StringToByteArray(key);
+            var saltBin = StringToByteArray(salt);
+
+            var encodedUrl = string.Join("/", WholeChunks(Convert.ToBase64String(Encoding.UTF8.GetBytes(url)).TrimEnd('='), 16));
+
+            var path = $"/{resize}/{width}/{height}/{gravity}/{enlarge}/{encodedUrl}.{extension}";
+
+            using (var hmac = new HMACSHA256(keybin))
+            {
+                var hash = hmac.ComputeHash(saltBin.Concat(Encoding.UTF8.GetBytes(path)).ToArray());
+
+                return $"/{Convert.ToBase64String(hash).TrimEnd('=')}{path}";
+            }
+        }
+
+        static byte[] StringToByteArray(string hex)
+        {
+            return Enumerable.Range(0, hex.Length)
+                             .Where(x => x % 2 == 0)
+                             .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
+                             .ToArray();
+        }
+
+        static IEnumerable<string> WholeChunks(string str, int maxChunkSize)
+        {
+            for (int i = 0; i < str.Length; i += maxChunkSize)
+                yield return str.Substring(i, Math.Min(maxChunkSize, str.Length - i));
+        }
+    }
+}