Added DPI parameter to ConverterOptions

Wkhtmltopdf.NetCore/Implementation/ConvertOptions.cs

@@ -11,9 +11,17 @@ public class ConvertOptions : IConvertOptions
     {
         public ConvertOptions()
         {
-            this.PageMargins = new Margins();
+            this.PageMargins = new Margins();
+            this.DPI = 96;
         }
 
+        /// <summary>
+        /// Change the dpi explicitly
+        /// </summary>
+        /// <remarks>Default value is 96</remarks>
+        [OptionFlag("-d")]
+        public int? DPI { get; set; }
+
         /// <summary>
         /// Sets the page size.
         /// </summary>