exercise ch 7
finish sign in
finish user edit, update, index, and destroy actions
complete updating users
unsaved changes
merge updating users
create the micropost model
first micropost validation
user/micropost associations
10.1.4 micropost refinements
10.1.5 content validations
finished 10.3.2; begin 10.3.3
finish 10.3.3
 Add user microposts
complete chap 10 exercises