QuizAttempt and ProblemAttempt models
Some tests exist for quiz attempts
Initial work to quiz attempt controller
Enrollments pass tests
Quiz Attempts Controller
Merge branch 'api-quizzes-rebased'
Merge branch 'master' into api-quiz-attempts

Conflicts:
	Gemfile.lock
	app/controllers/api/api_controller.rb
	app/models/user.rb
Enrollment and quiz attempts specs include user email

* User email is a constraint that was just added. Tests now correctly
  set that email field.
Quiz Attempts works with JSON problem_attempt input
Moved problem parsing code into the QuizAttempt model
Constructing quiz attempt with problems moved

* Now in quiz_attempt.rb
* seeds.rb now complete with examples
Clarifications in docs for enrollments and quiz_attempts
Merge branch 'master' into api-quiz-attempts
Fixed serializers to not include 'created_at'
Added comment to further describe enrollment model
Merge branch 'api-quiz-attempts'

Conflicts:
	Gemfile
	Gemfile.lock