Emit call stack for wkhtmltopdf errors.

src/core/error-handler.js

@@ -88,6 +88,7 @@ Error-handling routines for HackMyResume.
           case HACKMYSTATUS.wkhtmltopdf:
             msg = chalk.red.bold('ERROR: PDF generation failed. ') + chalk.red('Make sure wkhtmltopdf is ' +
             'installed and accessible from your path.');
+            if( ex.inner ) msg += chalk.red('\n' + ex.inner);
             break;
 
           case HACKMYSTATUS.invalid:

src/gen/html-pdf-generator.js

@@ -45,7 +45,7 @@ Definition of the HtmlPdfGenerator class.
       catch(ex) {
         // { [Error: write EPIPE] code: 'EPIPE', errno: 'EPIPE', ... }
         // { [Error: ENOENT] }
-        throw { fluenterror: this.codes.wkhtmltopdf };
+        throw { fluenterror: this.codes.wkhtmltopdf, inner: ex };
       }
     },