basic feature

* Requires set of ENV['BUNDLE_GEMFILE'] if run with bundle exec, otherwise not. Different from rag/grade3, which set ENV['RAILS_ROOT'] and now seems to not affect anything.

* Only seems to check the student archive, and not combine the standard solution with it first, so using a full app in that student_features.tar.gz file appears to work.
I would expect that has already been handled somewhere, didn't see it last night.

Sample code only disclaimer.
Copied same code to spec to demonstrate same needs if run with rspec or cucumber.
Backed off the refactoring, copy-pasted, etc. to make this a minimal set of changes for demonstration, communication.