Add docs Cloudfront cache invalidation

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>

@tiborvass @crosbymichael @tianon @fredlf @jamtur01 

right now, it assumes its going to be used only for docs updates, I'll continue to work on it in another PR for the full releases, and to try to get it to auto-detect the DISTRIBUTION_ID

Might want to add a bit about *how* to set it correctly, or where to get the info needed.