Prepare Website for the SFML 2.6 Release

[eXpl0it3r]

• [x] Update the changelog
  • [x] On the website
• [ ] Update the website
  • [x] Update the documentation
    • [x] Create a new doxygen script
    • [x] Generate new HTML documentation
    • [x] Apply the CSS overrides
    • [x] Adjust the documentation links
    • [x] Update the latest version (EN / FR)
  • [ ] Update the tutorials
    • [x] Duplicate the existing tutorial folder and rename for the new version
    • [x] Adjust the tutorial links
    • [x] Update the latest version (EN / FR)
    • [ ] Write / Adjust tutorials
      • [x] Replace sf::Quads in the TileMap tutorial
      • [x] Update event tutorial to mention scancodes
      • [x] Update real-time input tutorial to mention scancodes
      • [x] Add mention of SFML CMake Template (will be done separately: https://github.com/ChrisThrasher/SFML-Website/commit/668fdfed77ec30084e611a4f9095aa7635bf33a8)
      • [ ] Update CMake tutorial, for using GNU Install Dirs (especially macOS), see this comment
  • [x] Update the downloads
    • [x] Upload the new binaries
    • [x] Duplicate the existing download folder and rename for the new version
    • [x] Add or remove new or old compilers on the new download page
    • [x] Adjust the file sizes on the new download page
    • [x] Update the old version pages (EN / FR)
  • [x] Adjust rewrite rules to point to the latest version

Complete checklist: https://github.com/SFML/SFML/wiki/SD%3A-Releases

Code Updates: https://github.com/SFML/SFML/pull/2482

[eXpl0it3r]

If you see anything that was missed, please leave a comment on #163