Add evaluateScript option to evaluate custom script in the context of the web page

Author: alanpoulain

lib/scripts/pdf_a4_portrait.js

@@ -57,6 +57,9 @@ page.onLoadFinished = function (status) {
   // The paperSize object must be set at once
   page.paperSize = definePaperSize(getContent(page), options)
 
+  // Evaluate custom JavaScript
+  if (options.evaluateScript) page.evaluateJavaScript(options.evaluateScript)
+
   // Output to parent process
   var fileOptions = {
     type: options.type || 'pdf',