[test] Test jupyter book setup for builds

[mmcky]

This PR tests jupyter-book builds:

adds _toc.yml and _config.yml to support jb build ./ and removes index files.

Note: this is branched from manual-adjustments branch

[mmcky]

It seems that

sphinx:
  config:
    html_theme: quantecon_book_theme

doesn't override the theme. Is sphinx-book-theme inbuilt to juptyer-book?

[mmcky]

Ok so it looks like there is an issue when you add search to the _toc.yml that isn't nested in a folder.
It might clash with a default sphinx page generated out of context (??)

Reporting minimal example to jupyter-book here

[mmcky]

Closing test PR in favour of migration PR #63