Need to require the preview.rb file (at least for 1.9.2)
Since date change isn't going to get merged, I'm making it automatic since it's easier for me. ;)
Need to require compiler.rb as well.

Same as your last commit for previewer.rb, just for compiler.rb this time.  I've tested and it works.
Merge pull request #175 from binaryphile/patch-1

Need to require compiler.rb as well.
Merge branch 'master' of https://github.com/ruhoh/ruhoh.rb
Added error details to the folder config message.