Bump ruby version to 2.1.3.
Config class is responsible for saving settings.

When saving configuration settings it will check to see if a file
already exists that should be updated or if the file should be
created.
Add `test` command to run exercise test suite.

Only run test suite within an exercise dir.
Remove old spec helper.
Refactor challenge and lesson to use common base.
Return all submittable lessons.

Queries for challenges and exercises.
Add code to run rspec for exercises.
Generalize challenges to lessons.

In the context of the Horizon app, a lesson encompasses challenges,
exercises, articles, tutorials, etc.. Since this tool deals with
both challenges and exercises, use the term **lesson** to refer
to either one.
Display the lesson type.
Can submit either challenge or exercise.
Merge pull request #8 from LaunchAcademy/run_exercises

Run exercises