Add chained HTTP Proxy constructor (minio#276)

Fixes minio#273

Docs/API.md

@@ -62,6 +62,11 @@ __Secure Access__
 |---|
 |`Chain .WithSSL() to Minio Client object to use https instead of http. `   |
 
+__Proxy__
+
+|  |
+|---|
+|`Chain .WithProxy(proxyObject) to Minio Client object to use proxy `   |
 
 __Example__
 
@@ -78,6 +83,10 @@ MinioClient minioClient = new MinioClient("play.minio.io:9000",
                                           accessKey:"Q3AM3UQ867SPQQA43P2F", 
                                           secretKey:"zuf+tfteSlswRu7BJ86wekitnifILbZam1KYY3TG"
                                           ).WithSSL();
+
+// 3. Initializing minio client with proxy
+IWebProxy proxy = new WebProxy("192.168.0.1",8000);
+MinioClient minioClient = new MinioClient("my-ip-address:9000","minio","minio123").WithSSL().WithProxy(proxy);
 ```
 
 

Minio/MinioClient.cs

@@ -40,6 +40,7 @@ public partial class MinioClient
         // is the virtual style path or location based endpoint
         internal string Endpoint { get; private set; }
         internal string Region;
+
         // Corresponding URI for above endpoint
         internal Uri uri;
 
@@ -321,6 +322,16 @@ public MinioClient WithSSL()
             SetTargetURL(secureUrl);
             return this;
         }
+
+        /// <summary>
+        /// Uses webproxy for all requests if this method is invoked on client object
+        /// </summary>
+        /// <returns></returns>
+        public MinioClient WithProxy(IWebProxy proxy)
+        {
+            this.restClient.Proxy = proxy;
+            return this;
+        }
         /// <summary>
         /// Sets endpoint URL on the client object that request will be made against
         /// </summary>