UTM parameters
- http://blog.rafflecopter.com/2014/04/utm-parameters-best-practices
- http://blog.rafflecopter.com/2014/04/utm-naming-conventions
- https://www.ometria.com/blog/the-definitive-guide-to-utm-tagging-in-ecommerce
- http://www.terminusapp.com/blog/7-faqs-about-utm-parameters/
- http://www.bytefive.com/blogs/understanding-utm_source-utm_medium-and-utm_campaign
- https://blog.kissmetrics.com/how-to-use-utm-parameters/