docs: 2020 April Documentation Maintenance (#1484)

* Add doc page for Named Arguments

* Implement minor stylistic changes

* Update docfx.json to support NS2.0

Signed-off-by: Still Hsu <5843208+Still34@users.noreply.github.com>

* Fix broken xref in basic-operations

* Fix broken crefs

* Fix wordings in named argument

* Fix misleading warning about long-running code

* Fix misleading CommandService summary

Signed-off-by: Still Hsu <5843208+Still34@users.noreply.github.com>

* Update copyright year and version

Signed-off-by: Still Hsu <5843208+Still34@users.noreply.github.com>

* Escape example captions

* Add warning regarding FlattenAsync for GetReactionUsersAsync

* Fix a minor grammar mistake

Co-authored-by: Joe4evr <jii.geugten@gmail.com>

docs/docfx.json

@@ -9,7 +9,7 @@
     "dest": "api",
     "filter": "filterConfig.yml",
     "properties": {
-      "TargetFramework": "netstandard1.3"
+      "TargetFramework": "netstandard2.0"
     }
   }],
   "build": {
@@ -51,7 +51,7 @@
     "overwrite": "_overwrites/**/**.md",
     "globalMetadata": {
       "_appTitle": "Discord.Net Documentation",
-      "_appFooter": "Discord.Net (c) 2015-2019 2.1.1",
+      "_appFooter": "Discord.Net (c) 2015-2020 2.2.0",
       "_enableSearch": true,
       "_appLogoPath": "marketing/logo/SVG/Logomark Purple.svg",
       "_appFaviconPath":  "favicon.ico"