[TEST] Added an integration test for combining pagination with scopes

See: http://guides.rubyonrails.org/active_record_querying.html#scopes

Related: #16
Fixed the incorrect behaviour of limit() and page() methods

Previously:

  When klass.default_per_page is 25,

  response.limit(35).page(3)
  => :size is back to 25, :from is 25 * 2

  response.page(3).limit(35)
  => :size is 35, but :from is 25 * 2

After this patch:

  response.limit(35).page(3)
  => :size is 35, :from is 35 * 2

  response.page(3).limit(35)
  => :size is 35, :from is 35 * 2

Closes #42

Related: #72, #55