Strong, shallow ETags by default

See http://bitworking.org/news/150/REST-Tip-Deep-etags-give-you-more-benefits
for the difference between shallow and deep ETags.

Set sensible caching policies

See http://tools.ietf.org/html/rfc7234

https://www.pivotaltracker.com/story/show/72952306
[Meh](https://code.google.com/p/selenium/issues/detail?id=141).

I'll add something to pp-smokey instead. Happy for this to be reviewed.