Add User model that uses has_secure_password
Add ability to sign in.
WIP
Associate user to post and show associated user on post display
Fix tests that broke after associating user to post
Merge branch 'master' into ben-week-four

Conflicts:
	app/models/post.rb
	config/routes.rb
	db/schema.rb
	spec/features/deleting_a_comment_spec.rb
	spec/features/viewing_comments_spec.rb