Used form_tag in place of form_for.
 Used a custom RSpec matcher to decouple the tests from the implementation.
Used let-command to organize string of "Sign in" and "Sign out"
Adjusted indent
Rejected sessions hash in new.html.erb.
And rewrote sessions controller to adjest some codes.
Fixed: changed ":class =>" into "class:"
Rollbacked
Merge pull request #11 from Tacahilo/exercise_8_5_1

Rails Tutorial Exercise 8.5.1のレビューのお願い