Updated API Protocol (markdown)

API-Protocol.md

@@ -156,15 +156,34 @@ Messages bodies sent and received by clients are a protocol buffer structure:
 
 ```
 message PushMessageContent {
-  optional string body = 1;
-
   message AttachmentPointer {
-    optional fixed64 id = 1;
-    optional string contentType = 2;
-    optional bytes key = 3;
+    optional fixed64 id          = 1;
+    optional string  contentType = 2;
+    optional bytes   key         = 3;
   }
 
+  message GroupContext {
+    enum Type {
+      UNKNOWN = 0;
+      UPDATE  = 1;
+      DELIVER = 2;
+      QUIT    = 3;
+    }
+    optional bytes             id      = 1;
+    optional Type              type    = 2;
+    optional string            name    = 3;
+    repeated string            members = 4;
+    optional AttachmentPointer avatar  = 5;
+  }
+
+  enum Flags {
+    END_SESSION = 1;
+  }
+
+  optional string            body        = 1;
   repeated AttachmentPointer attachments = 2;
+  optional GroupContext      group       = 3;
+  optional Flags             flags       = 4;
 }
 ```