Remove only one page from cache

Added

• Added support to pass CACHE_EXPIRATION_TIME environment variable

Changed

• Only the Clear-Site-Data: * header purges all cache now
• The Cache-Control: must-revalidate header removes only one page instead of flushing all caches

Purge prerender cache

Added an ability to purge prerender cache by sending specific headers on the request

First release

• Taken https://github.com/goprerender/prerender as a base
• Added support to pass STORAGE_URL environment variable
• Dockerized goprerender server and storage
• Added docker-compose example and Makefile commands for faster setup