create micropost model with content and user_id attributes
refactor destroy method for user controller
add micropost model
add more tests
ensures microposts are returned in order, and that a user's microposts are deleted with its user
validates that micropost content exists and is no longer than 140 characters
shows a user's microposts
seed microposts and style micropost displays
restrict creating and deleting of microposts to signed in users
add micropost text form