Added FileName property for Picture

DocX/Picture.cs

         private string name;
         private string descr;
         private int cx, cy;
+        private string fileName;
         private uint rotation;
         private bool hFlip, vFlip;
         private object pictureShape;
                 select a.Value
             ).First();
 
+
+            this.fileName =
+            (
+              from e in Xml.Descendants(XName.Get("cNvPr", "http://schemas.openxmlformats.org/drawingml/2006/picture"))
+              select e.Attribute("name").Value
+            ).First();
+
             this.descr =
             (
                 from e in Xml.Descendants()
             } 
         }
 
+        ///<summary>
+        /// Returns the name of the image file for the picture.
+        ///</summary>
+        public string FileName
+        {
+          get { return fileName; }
+        }
+
         /// <summary>
         /// Get or sets the Width of this Image.
         /// </summary>