+ Some contributions from @purpledank

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

* 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

Closes #1074

This code was not referenced anywhere in the active codebase.

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

Improve XML docs for commands quotation mark aliases feature

* fix channel permissions modify parameter to use nullable boolean, correct default value

* Add general tests for the ChannelPermissions.Modify method to test default values

* remove unused cast in tests

* add guildpermission modify no param tests

* Add no-param modify tests for OverwritePermissions

* fix inconsistent parameters in GuildPermissions cstr

* Adjust formatting of methods and cstrs with many parameters

* remove temp file that was included. no idea what that is

* Fix System dependency

I should really stop fixing merge conflicts in the github website.

* Fix #995 ICategoryChannel.CategoryID throws NotSupportedException

* Add tests

* change run mode of TestChannelCategories

* Add throw for GetCategoryAsync

* Add xml doc explaining why exception is thrown

* Add test coverage for text and voice channel categories

* initial implementation of INestedChannel

* more implementation of INestedChannel design

* Add case in RestChannel Create for Category type

* set the CategoryID for RestVoiceChannel

* rewrite channel category tests to work with existing pattern

* remove outdated todo

* Make IVoiceChannel implement INestedChannel

* remove redundant interface implementation

* Add c#7 feature from feedback

* Remove redundant GetCategoryAsync methods from socket entities

* Added configureawait to async methods

* change signature of interface GetCategoryAsync

* Add check for cachemode in rest channel GetCategory

* remove redundant IGuildChannel interface from ITextChannel and IVoiceChannel

- Fixes indentation with a few files (looks like a bad copy+paste job)
- Renames RoleInfo to RoleEditInfo
- Moves RoleInfo from MemberRoleAuditLogData into its own class

All of this should improve docs.

- Replaces the usages of `ReadMessages` with `ViewChannel`
- Renames the read message parameters of `GuildPermissions#Modify` to be view channel as well