Support ESI/SSI includes #50

We've got a project that could really benefit from ESI for performance. Is there any documentation for this?

Nothing public yet, but plan on having something in next week or so.

FWIW, out implementation is RFC compliant with the ESI 1.0 spec, so there really isn't anything Craft or Craft Cloud specific here.

To make them easier to work with, we plan on providing a Twig tag that can fall back to regular include when not in a Craft Cloud environment (e.g. working locally).

I'll post some rough examples here today if you want to start playing around before we have official docs.

@andrewfairlie sorry for the wait! Here's a rough example of how you can use ESI's: https://gist.github.com/timkelty/f9553c457abd37bcc3b31253e6301d60

Note: we'll soon be providing some helpers so you won't need to do the kind of include fallback I'm showing in the example to work locally.