* feat: add content slot functionality for templates and components

* Refactor to support full slot contexts with internal transformations

* Refactor the `smartify` filter so it doesn't rely on a converter

Closes #401

* bugfix

* cop fixes

* Support slots in generated pages

* Add documentation for slotted content in templates

* Add slot tests to template engines feature

* Add source docs, tests for content slots

* Add additional documentation around slot content