* Add ETag header. * Comply with RFC 7232. * Moved logic into httpcache.go * Changed name. * Lint * Implemented If-None-Match list. * Fixed missing header on * * Removed weak etag support. * Removed * support. * Added unit test. * Lint Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com> Co-authored-by: techknowlogick <techknowlogick@gitea.io>