Quantecon-book-theme

This release checks for the presence of the `_notebooks` directory to show the download button.

This release has a few enhancements:
- center aligning figures, supporting output_scroll tag
- countering pyLDAvis package stylesheet overwriting

This release has added codecov token explicitlt in codecov.yml , as codecov was complaining about it.
It also has following two features:
- Checking for mathjax version and using the config specified in `layout.html` when mathjax is of version 3. Users can use `mathjax_config` variable in `_config.yml` for version 2.
- Left-hand side menubar can now be made persistent across web pages using a config variable.

This release has fixes for the downlodPDFModal functionality and styling.

Has the following features and fixes:
- Collapsible input code blocks
- private input field in the launch dropdown menu for custom jupyterlab servers.
- mathjax config reading issue
- google analytics fix

Has the following fixes:

- Home button takes us to the global home page.
- Images in the lectures under the theme contained inside the margins.
- Correct font colors for dark mode.
- \boldsymbol tex package inclusion in mathjax.