Quantecon-book-theme

**Full Changelog**: https://github.com/QuantEcon/quantecon-book-theme/compare/v0.7.0...v0.7.1

This release introduces two new features:

1. Styling and adding functionalities to the margin directive inherited from sphinx-book-theme, to make it useable in this theme.
2. Adding the ability to add author names with hyperlinks to their bio using config variable, in the main toc page. And also the ability to control its font size with a config.

This release gives the support to include a dark mode version of the logo. By storing it in the static folder, and specifying it using a config variable.

This release included styles enhancements and changes for the dark theme.

Refactoring of the project to use pyproject.toml instead of setup.py, and sphinx-theme-builder as the build backend.