* Add EditorConfig

* Add basic .NET style rules

* Add naming rules

* Add some more extension

* Add target of the internal fields

* Fix build fails when built on macOS and Linux

* Use 'Condition' attributes

refs: 6f29dda78b (r181371650)

* added UserDefaultAvatar to IUser

* pass ushort as discriminator

* removed unneeded ushort.parse

* Create new entities on each build call. Added Length property to EmbedBuilder.

* Resolve Length issues per #1012

+ This commit also adds overwrites for CommandContexts; this allows for additional remarks for the class.

* Throw when attempting to modify a message not made by the current user

* Didn't realize the client is passed into the MessageHelper function

* Respond to feedback

* Update Users property for category channels

* Wrong property being used for Channels property

CategoryId is the category that "owns" this channel. That is actually impossible right now for category channels, so it returns null and get all channels wrongly.

* Resolve permissions for category

* Remove spaces

* Small fix for IChannel.GetUsersAsync

To many files.

+ GameAsset
+ GameTimestamps
+ Format

* Fix comments to comply with third-person commenting style
+ Various attributes
+ Various Command-related objects
+ Many more

+ ActivityType
+ IAttachment
+ ChannelPermission
+ ChannelPermissions
+ ChannelType
+ Attachment

+ EmbedBuilderExtensions
+ CacheMode
+ ImageFormat

+ DiscordConfig
+ CDN
+ MentionUtils
+ LogMessage
+ LogSeverity

This resolves #987

Previous behavior was that even if `null` was passed for an embed in
UploadFileAsync, the Embed property on UploadFileArgs was still
specified - this meant we were always sending a payload_json.

If a payload_json is specified, it seems like Discord will only read
from the payload_json, and will ignore properties set outside of it.

To prevent unnecessary code duplication, this commit always specifies
parameters in the payload_json, and also will only include the embed if
one was actually specified with real data (not null).

* UnixTimestampConverter should now obey a maximum value

This change prevents an issue where the converter would be unable to
handle obscenely large timestamp values - which are actually quite
common on Discord.

OptionalConverter had to be rewritten to support checking whether or not
an InnerConverter returned an Optional. The perf impacts from this
_shouldn't_ be too bad, as types without a custom parser (which should
be the majority of Optionals in the lib) will bypass the type-check.

* optimizations on OptionalConverter

- Add a helper under CDN for cover art URLs
It would be bad practice of us to leave CDN urls hardcoded in the
deserializer, would be harder to change down the line should Spotify
ever change their CDN.

I'm not entirely supportive of leaving Spotify's CDN hardcoded in our lib
either, but there's no better alternative.

- Change SpotifyGame#Artists to an IEnumerable<string>
Seems pretty common to prefer IEnumerables in place of Arrays.