core: Continue PieCrust3 refactor, simplify pages. The asset pipeline is still the only function pipeline at this point. * No more `QualifiedPage`, and several other pieces of code deleted. * Data providers are simpler and more focused. For instance, the page iterator doesn't try to support other types of items. * Route parameters are proper known source metadata to remove the confusion between the two. * Make the baker and pipeline more correctly manage records and record histories. * Add support for record collapsing and deleting stale outputs in the asset pipeline.

---
title: Code
---

PieCrust can be extended with plugins in order to support additional features
such as new [formatters][1], [processors][2], or [template engines][3] (among
other things).

[Creating a plugin][4] is very easy in itself, but requires making a
`setuptools` package in order to be easily shared with other people.


[1]: {{docurl('content/formatters')}}
[2]: {{docurl('asset-pipeline')}}
[3]: {{docurl('content/templating')}}
[4]: {{apiurl('plugins')}}