ETags

Add support for the HTTP Protocol's ETags which enable end users to cache anonymous requests and thus reduce origin load and increase client responsiveness.

Documentation on the RFC can be found here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.19

An implementation of ETags can be found in the GDATA API v2.0: https://developers.google.com/gdata/docs/2.0/reference#ResourceVersioning

Google is shifting their API resources around so there's a deprecated warning on this page but the section on ETags is current: