worked on sessions, added logging out to users, created a sign in from the home page.
added doctors controller with failing tests for get, show actions
added doctors, patients via single table inheritence from user. added type to user db.
doctors, patients sign in via single table inheritance.
userscontroller is now the superclass of doctorscontroller
sign out tests are passing.
current users profile page link now in header. current users can only see their own profile page. users not signed in can't see anyone's profile (todo: make doctor profiles public.)
merge conlict resolved. going with header layout from 'doctors' branch.