AppVeyor has released support for targetting Ubuntu 18.04 environments.
This adds Ubuntu to the list of build images for Appveyor to use.

this was the name change i always wanted

This adds the following property to ITextChannel
- SlowMode (int)

The SlowMode field defines the time in seconds users must wait between
sending messages; if zero, slow-mode is disabled.

Bots are not affected by slow-mode, and as such, no changes need to be
made to the REST client's internal ratelimiting. This is strictly a
read/write cosmetic property for bots.

* Fix swapped parameters in ArgumentException and ArgumentNullException cstrs

The constructors of ArgumentException and ArgumentNullException are inconsistent with each other, which results in their parameters being swapped here and there.

* Use named parameters for ArgumentException constructors

Cleans up some of the methods of EmbedBuilder to use simpler syntax as well

* Change all Select(... as ...) to OfType

* Add changes according to 194a8aa427

* Add input validation for bot tokens based on their length

* Add token validation to BaseDiscordClient#LoginAsync

Adds a TokenUtils class which is used to validate that tokens are correct

* Revert changes to DiscordRestApiClient

* Add Unit tests to the TokenUtils class, fix a logic error that was caught by those tests

* Allow for API to throw exceptions

Moves the validation of tokens to be inside of LoginInternalAsync, and writes a Warning to the console when the supplied tokens are invalid

Should fix issues in audit logs when deserializing overwrites and
similar types which we use a custom contract resolver for.

Nullable<T> is not valid for Attributes, this is my suggested fix.

* Initial commit

* Add alternative suggestion

* Fix typo

* Update README.md

* Don't attempt instantiation of an abstract module
* Attempt associating a TypeReader in case one is registered late (ie. OnModuleBuilding)

* Added GetJumpUrl() as an IMessage extension method

* Removed extra line for consistency

* Moved the namespace from Discord.Commands to Discord

* lint: remove eof newline

* lint: use TextChannel to get GuildID

This dispatch is undocumented and only used by user accounts.

* Mark guild as optional for invite

* Mark partial InviteMetadata members as Optional<T>

* Some of them aren't sent when requesting through the general GET invite endpoint

* Remove GetInviteParams

* It was kinda stupid in the first place, might as well always get the count instead of having to ask the user whether they want the two fields filled or not.

* Add ChannelType property

* Add vanity invite support

* Solved 4003 Authentication Error (Race Condition)

* Set static interval & removed hello case

* 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