Cleaned up `base.Handler`, reducing many property accessor functions to lambdas for cleaner code. Refactored template rendering from `handler.render`, eliminating needless merges for template context and headers. Fixed an issue where the Response object could be re-created and data from the previous response partially lost.
Refactored and cleaned up runtime hooks, which now build context incrementally as they go instead of vomiting kwargs :sparkles: and completely eliminated `content.ContentFilter`, which didn't really filter content. So it has been replaced with `hooks.HookResponder`, and a new partner, `hooks.Context` (which allows selecting context arguments to be passed to the selected hook).
Cleaned up generators for render flow.