Make PaperFormat Height and Width public. (#408)

* Make PaperFormat Height and Width public.

* Nit

Author: kblok

lib/PuppeteerSharp/Media/PaperFormat.cs

@@ -6,15 +6,24 @@
     /// <seealso cref="PdfOptions.Format"/>
     public class PaperFormat
     {
-        internal decimal Width { get; set; }
-        internal decimal Height { get; set; }
-
         private PaperFormat(decimal width, decimal height)
         {
             Width = width;
             Height = height;
         }
 
+        /// <summary>
+        /// Page width in inches
+        /// </summary>
+        /// <value>The width.</value>
+        public decimal Width { get; set; }
+
+        /// <summary>
+        /// Page height in inches
+        /// </summary>
+        /// <value>The Height.</value>
+        public decimal Height { get; set; }
+
         /// <summary>
         /// Letter.
         /// </summary>