* push: Implement HTTP/2 server push (close#3551)
* push: Abstract header ops by embedding into new struct type
This will allow us to add more fields to customize headers in
push-specific ways in the future.
* push: Ensure Link resources are pushed before response is written
* Change header name from X-Caddy-Push to Caddy-Push
This is temporary as we prepare for a stable v2 release. We don't want
to make promises we don't know we can keep, and the Starlark integration
deserves much more focused attention which resources and funding do not
currently permit. When the project is financially stable, I will be able
to revisit this properly and add flexible, robust Starlark scripting
support to Caddy 2.
This makes it easier to make "standard" caddy builds, since you'll only
need to add a single import to get all of Caddy's standard modules.
There is a package for all of Caddy's standard modules (modules/standard)
and a package for the HTTP app's standard modules only
(modules/caddyhttp/standard).
We still need to decide which of these, if not all of them, should be
kept in the standard build. Those which aren't should be moved out of
this repo. See #2780.