* improve versioning of the documentation website
* fix version dropdown menu
* fix linter errors
* hide contribuiting subsections and update site/build_docs.py
* revert changes contributing section and remove unwanted text
* add navbar-version-selector.html
* update site/build_docs.py
* update site/build_docs.py
* update _index.html and fix mistakes in config.toml
* fix _index.html
* replace all tabs with spaces
* update navbar-version-selector.html
* fix link in the site/readme.md
* replace tabs with spaces in custom.scss and 404.html
* fix linter errors