added validations for password_confirmation presence, and email regex and uniqueness
rewrote rspec tests for users
added validation of presence for question_id and user_id
added shoulda rspec tests for answer
added validation for presence of user id
added validation tests for question model
added validation of presence for best answer
added validations for presence for :text, :commentable_id, :commentable_type, :user_id
added rspec tests for comments, question tags, tags, and vote models
reformatted tag