* Update the contributors list.
* Update the version number.
* Sync zh and zh-hant versions.
* Move epub builder to the utils branch.
* Optimize all figure files using pngquant.
* Update copyright.
* Update Acknowledgements.
* Update buttons in README.
* Fix the logo in the en version
* Optimize header color and fix body background color
* Update theme switch's name
* Fix backfrop-filter on Safari
* Update some animation's file name for adding egde when cropping
* Re-count the comments number
* A bug fix in n_queens_problem.md