docs: September 2019 Documentation Update (#1379)

* docs: adjust wording of ActivityType.Watching enum

Adjusts the xmldoc summary wording of the ActivityType.Watching enum to
fix a wording issue.

* Add D.NET Logo to Open Graph meta tags

* Update DescriptionGenerator
...And update color to suit the logo better

* Disable smooth scrolling due to user complaints

* Remove unnecessary spacing in sideaffix

* Update footer version

* Remove featherlight plugin

As it is unnecessary and can break image tags

* Adjust wordings regarding safe-handling of secrets

* Fix formatting for first bot token sample

* Add badges to homepage

* Minor wording fixes on terminal

* Update to higher quality PNG

* Add Discord.Net.Example in sln for build validation

* Clarify all instances of IAsnycEnumerable

* Clarify overridden props in SocketNewsChannel

* Add returns and params docs for SyncPermissionsAsync

* Remove/fix invalid XMLdoc strings

* Remove AppVeyor and add GitHub badge

docs/docfx.json

@@ -35,7 +35,8 @@
         "**/images/**",
         "**/samples/**",
         "langwordMapping.yml",
-        "marketing/logo/SVG/**.svg",
+        "marketing/logo/**.svg",
+        "marketing/logo/**.png",
         "favicon.ico"
       ]
     }],
@@ -50,7 +51,7 @@
     "overwrite": "_overwrites/**/**.md",
     "globalMetadata": {
       "_appTitle": "Discord.Net Documentation",
-      "_appFooter": "Discord.Net (c) 2015-2019 2.0.1",
+      "_appFooter": "Discord.Net (c) 2015-2019 2.1.1",
       "_enableSearch": true,
       "_appLogoPath": "marketing/logo/SVG/Logomark Purple.svg",
       "_appFaviconPath":  "favicon.ico"