Show pandoc errors

[candlerb]

At the moment if pandoc fails, no error is shown.

Suggested simple patch:

--- a/lib/jekyll-pandoc-multiple-formats.rb
+++ b/lib/jekyll-pandoc-multiple-formats.rb
@@ -56,6 +56,7 @@ class PandocGenerator < Generator
         Open3::popen3(pandoc) do |stdin, stdout, stderr|
           stdin.puts content
           stdin.close
+          STDERR.puts stderr.read
         end

         # Skip failed files
@@ -101,6 +102,7 @@ module JekyllPandocMultipleFormats
             stdin.close

             output = stdout.read.strip
+            STDERR.puts stderr.read

           end

As a demonstration, use the default jekyll site and add to _config.yml

pandoc:
  skip: false
  outputs:
    pdf:
    epub:

With this patch you can see the failures:

Brians-MacBook-Air:my-awesome-site $ jekyll build
Configuration file: /Users/brian/tmp/my-awesome-site/_config.yml
            Source: /Users/brian/tmp/my-awesome-site
       Destination: /Users/brian/tmp/my-awesome-site/_site
      Generating... Creating /Users/brian/tmp/my-awesome-site/pdf/jekyll/update/2013/11/20
pandoc  -o /Users/brian/tmp/my-awesome-site/pdf/jekyll/update/2013/11/20/jekyll/update/2013/11/20/welcome-to-jekyll.pdf
pandoc: /Users/brian/tmp/my-awesome-site/pdf/jekyll/update/2013/11/20/jekyll/update/2013/11/20/welcome-to-jekyll.pdf: openBinaryFile: does not exist (No such file or directory)
Creating /Users/brian/tmp/my-awesome-site/epub/jekyll/update/2013/11/20
pandoc  -o /Users/brian/tmp/my-awesome-site/epub/jekyll/update/2013/11/20/jekyll/update/2013/11/20/welcome-to-jekyll.epub
pandoc: /Users/brian/tmp/my-awesome-site/epub/jekyll/update/2013/11/20/jekyll/update/2013/11/20/welcome-to-jekyll.epub: openBinaryFile: does not exist (No such file or directory)

done.

[candlerb]

Actually STDERR.print is better than STDERR.puts so you don't get unnecessary blank lines shown when all is working.