The documentation was not reflecting that the latest change to
html.home_page_in_navbar sets the value to be true by default, rather
than false.

https://github.com/executablebooks/jupyter-book/commit/4d886b47a3889842f130ab17450530696592f407

This commit also split apart a note that were about two unrelated
points.

Closes #992

Co-authored-by: Chris Sewell <chrisj_sewell@hotmail.com>

See commits for details; mainly centred around config validation and pdf builds

require.js must be loaded on the page

Otherwise the margin directive is not available for LaTeX builds

This adds a `--cookiecutter` option to `jb create`, to allow users to use the [Jupyter Book cookiecutter](https://github.com/executablebooks/cookiecutter-jupyter-book

) to create a book template:

```console
jupyter-book create --cookiecutter mybookpath/
```

Co-authored-by: Chris Sewell <chrisj_sewell@hotmail.com>

This merge contains the majority of the changes for the v0.8.0 release.
See the individual commits and CHANGELOG.md for details.

Redirect old content-types pages to file-types

jupytext v0.16 now properly integrates with myst-parser>=0.12

The sphinx-panels sphinx extension has been added to the base jupyter-book distribution, and its use documented.

Some other minor documetation updates have also been applied

The generation of sphinx config has been consolidated into a single entry point: `jupyter_book.config:get_final_config`, where before it was spread over yaml.py and sphinx.py, making it difficult to determine what the finaly configuration would be.

This now allows for proper testing of the configuration generation, added in tests/test_config.py, which also clarified some bugs identified in #915. These have now been fixed.

Finally this has also allowed for the addition of a `jb config sphinx` command, which generates the a Sphinx conf.py representation of the build configuration.
This should help advanced users/maintainers to understand/debug builds.

Co-authored-by: Chris Holdgraf <choldgraf@berkeley.edu>