[Review] Request from 'vlewin' @ 'vlewin/e-shop/review_140618_improve_test_coverage'

Please review the following changes:
  * 7c62c81 Update README.md
  * c2d981a Update README.md
  * 417b30d improve model test coverage
  * 1800a47 clean up
  * a8c8c67 add timestamps to cart
  * 4054f5d add more factories
  * ebfc90c add category model test
  * 563f2a4 add address model test
  * 14673dd replace debugger with byebug and add shoulda gem
  * 488f572 add order and shipment factory
  * 142a8aa update README
  * e142062 test user model
  * c853e26 require reails_helper in specs and fix routing tests
  * 2408646 rename store controller spec
  * d2a38fc first address is a default one
  * b412db5 add user factory and update address factory
  * d07cf3c set up Spring, Rspec and Guard