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

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

Also, fix examples (tag syntax, remove redundant nested `md` blocks).

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

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

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>