Fix HHVM on Travis by using FastCGI instead of built-in webserver
Merge pull request #65 from FriendsOfSymfony/hhvm-3

Fix HHVM on Travis by using FastCGI instead of built-in webserver
Improve user context caching docs (fix #59)
Unset req.http.X-FOSHttpCache-TempCookie
Fix errors and rename HTTP headers
Fix variable name
Fix syntax highlighting
Note that application not Varnish sets Vary header
Fix whitespace and rename HTTP headers