+ Some contributions from @purpledank

* Change passive voice in "Get Started" to active
* Fix improper preposition in Commands Introduction page
* Fix minor grammar mistakes in "Your First Bot" (future tense -> present tense/subjunctive mood -> indicative mood/proper noun casing/incorrect noun/add missing article)
* Fix minor grammar mistakes in "Installation" (missing article)

* Changed the path from 'lastmodified' to 'last-modified' for consistency

* Moved theme-switcher code to scripts partial file
+ Add author's MIT license to featherlight javascript

* InvalidPathChars does not exist in NS1.3; replaced with GetInvalidPathChars instead.

+ Add precondition usage sample
+ Add precondition group usage sample
+ Move precondition samples to its own sample folder

+ Fix various formatting.
+ Provide a more detailed walkthrough for dependency injection.
+ Add C# note at intro.

* ConnectAsync(bool external) API implemented

This allows developers to handle the AudioClient externally (for example with Lavalink)

* Modify ConnectAsync API and add DisconnectAsync to IAudioChannel

* Update summary message on IAudioChannel.DisconnectAsync()

* Review changes:
- Fix `if (!external)` styling
- Remove unecessary ConnectAsync overload

* SocketVoiceChannel overload update

* Update IAudioChannel.ConnectAsync()
- Remove ConfigAction from parameters
- Add SelfDeafen/SelfMute to parameters

* Remove SocketVoiceChannel.ConnectAsync() default params (Inherit)

some guilds aren't on g250k yet? not sure

Forgot to hit save properly... Whoops.

Closes #1074

This code was not referenced anywhere in the active codebase.

Use (actual, expected) format for Assert.Equal, fixes analyzer warnings

Discord no longer treats channels prefixed with 'nsfw' as NSFW,
so we no longer need to have this check.

This reverts commit adf4da19fc.

Someone hasn't written c# in a while