Coltrane

- Ability to [configure cache](env.mdcache).
- Allow content or data directory to be specified [48](https://github.com/adamghill/coltrane/issues/48).
- Fix: Handle invalid JSON data [48](https://github.com/adamghill/coltrane/issues/48).

- If a markdown file with a slug cannot be found, look for a template with the same slug. Special case for `*.html` which can be a fall-back option to render for any slug.
- Add `raise_404` template tag.
- Add `last_path` template tag.

- Support Django template tags with the `mistune` markdown renderer.

- Include extra files when building the static site.

- Add `EXTRA_FILE_NAMES` setting to support serving static files like `robots.txt`.

- Add support for rendering markdown with `mistune`. See [MARKDOWN_RENDERED](settings.md) for how to enable. `mistune` will be the default renderer after 0.22.0 because it is 1) faster rendering markdown than `markdown2`, 2) enables new functionality like `abbr`, 3) fixed a bug in the generation of the tables of contents HTML, and 4) has a plugin architecture to add new features.
- Improve table of contents rendering for `mistune`.