Reaffirm string-based generation.

In recent commits, HackMyResume generation logic, much like the pilots
in Top Gun who became too reliant on air-to-air missiles and lost the
true art of dogfighting, has become dependent on file-based generation
as implicit file assumptions have crept in. This commit reaffirms the
file-less, string-based nature of the generation process and, as a side
effect, adjusts the behavior of (binary) PDF generation to match.

src/gen/html-pdf-generator.js

@@ -23,8 +23,8 @@ Definition of the HtmlPdfGenerator class.
     Generate the binary PDF.
     */
     onBeforeSave: function( info ) {
-      pdf(info.mk, info.outputFile);
-      return info.mk;
+      pdf( info.mk, info.outputFile );
+      return null; // halt further processing
     }
 
   });