Ask for Rails.logger first

ref #57
A quick solutions is ask first for the logger, but the real issue is that the all the methods of configurations https://github.com/whichdigital/active-rest-client/blob/master/lib/active_rest_client/configuration.rb makes a call to a logger before load the rails Logger.

Another Possible soluction is ask on each method if i want to log the change, something like 

```ruby
module ActiveRestClient
  module Configuration
    module ClassMethods
      def base_url(value = nil, log=false)
        #code for base url method
      end
     end
  end
end
```