chore: move site from Tygo-van-den-Hurk.github.io to js.org

The js.org domain is shorter and makes `Slyde` not a subdirectory site. I
also think it looks more professional. Can be merged when they merge pull
request js-org/js.org#10514 into master.

Author: Tygo-van-den-Hurk

mkdocs.yml

@@ -1,6 +1,6 @@
 site_name: Slyde
 site_author: Tygo van den Hurk
-site_url: https://tygo-van-den-hurk.github.io/Slyde/
+site_url: https://slyde.js.org/
 site_description: Make beautifully animated Slydes and presentations from XML with ease!
 
 repo_url: https://github.com/Tygo-van-den-Hurk/Slyde