Kilt is unmaintained and the ECR templating logic has been
natively integrated into Kemal with the issues previously seen
having been resolved.
This commit is mostly a precursor to support the next Kemal
release which will add the ability to create error handlers for
raised exceptions.
See https://github.com/kemalcr/kemal/pull/688
Directly using Crystal's ECR seems to be causing issues, so
don't use kemal's 'render' macro and patch 'content_for' to
have the same behavior as before Kemal v1.1.1
