Add rspec-rails

RSpec 3 will be released soon, so we don't need to use or learn old one.
be rails generate rspec:install
Add database_cleaner

database_cleaner will delete all entries in database before each example.
With this, we can avoid data conflict between examples.
Change default format to `documentation`

With this, rspec command will output full documentation of each
specs instead of dots. This is useful to know what's happening
in our specs.
Add first spec
Add .travis.yml
Compare times with `#to_i`

`Time` is compared by fractional.
http://railsware.com/blog/2014/04/01/time-comparison-in-ruby/