Better support for testing

[doutatsu]

As I was writing tests for the scraper I've made, I've realised its not super straightforward at the moment. It would be great to improve on that front:

1. Add testing section to the documentation, showcasing how to set it up and test in Rails for example
2. Expand global configuration options. I would have liked to be able to disable delay globally in the test environment, instead of doing this in every scraper I write: @config = { before_request: { delay: 1..2 } } unless Rails.env.test?
3. Add automatic detection of the test environment. Currently I have to manually set it in the rails_helper: ENV['KIMURAI_ENV'] ||= 'test'

[rubyFeedback]

I think it may be easier to split this into separate suggestions. 3) sounds fairly easy I think, though.