Add Micropost model.
Add initial micropost specs per listing 10.2.
Migrate micropost.
Add validity tests per listing 10.3.
Validate :user_id presence per listing 10.4.
Modify micropost specs per listing 10.5.
Add associations per listings 10.7 and 10.8.
Modify factories.rb per listing 10.9.
Test micropost order per listing 10.10.
Fix typo.
Fix typo.
Order microposts per listing 10.11.
Test that associated posts are destroyedd per listing 10.12.
Modify user model so that associated posts are destroyed per listing 10.13.
Fix syntactic error.
Add micropost validation tests per listing 10.14.
Validate micropost content per listing 10.15.
Change 'minimum' to 'maximum'.
Test user-page micropost content per listing 10.16.
Add microposts to user show.html.erb per listing 10.17.