Statistics from Altmetric.com
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.
Author note In the reference list papers with a * are highlighted as a key reference.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.