New docs site built with 11ty.js

[michaelhthomas]

Overhaul of the site which adds the following:

• New docs site, which will contain the user-facing guides and information for Zim
• Static site built with 11ty.js using Github Actions and hosted on Github Pages
• New docs to make the best use of the new docs site and give an introduction to newcomers
• Updated landing page with new animations courtesy of @ericbn
• Tentative new logo in the navbar