Improve and modernize docs. (#2882)

* Add proper home landing page.

* Improve landing page considerably.

* Add navbar library name.

* Fix css rules.

* Update getting started images.

* Change favicon to the navbar's logo.

* Tiny change to docs index.

* Add title to home landing page.

* Tweak build overrides faq page.

* Fix FAQ article titles and headers.

* Fix FAQ article titles and headers.

* Replace channel 9 with the official .net course.

docs/docfx.json

@@ -39,7 +39,7 @@
           "langwordMapping.yml",
           "marketing/logo/**.svg",
           "marketing/logo/**.png",
-          "favicon.ico",
+          "favicon.png",
           "../src/Discord.Net.Examples/**.cs"
         ]
       }
@@ -58,10 +58,11 @@
     "overwrite": "_overwrites/**/**.md",
     "globalMetadata": {
       "_appTitle": "Discord.Net Documentation",
+      "_appName": "Discord.Net",
       "_appFooter": "Discord.Net © 2015-2024 3.13.1",
       "_enableSearch": true,
       "_appLogoPath": "marketing/logo/SVG/Logomark Purple.svg",
-      "_appFaviconPath": "favicon.ico"
+      "_appFaviconPath": "favicon.png"
     },
     "xref": ["https://github.com/dotnet/docfx/raw/main/.xrefmap.json"]
   }