+ This change requires us to target the solution.
+ Due to docfx issues, we must specify a  upon metadata compilation.
    - Because of this, docfx may complain about missing targets.
    - If we don't target a specific TargetFramework, docfx will fail to recognize documents with multiple framework targets.
    - Further investigation may be required.

* 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

* Add guide for building the docs

* Add version to the footer of the docs

* fix links for readme

* change formatting of doc build readme

* proper capitalization of DocFX in readme

* Remove code tags around version

To many files.

Notable changes include the following,

+ Add _services into  examples.
+ Rename Commands back to commands.
    - This was changed in my previous PR; however, this made readability really weird.
+ Fix broken examples.
+ Directly referencing anchors instead of saying 'see this below'

+ 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

+ Modified the headings to fit the formal aspect of docs.
+ Added more details regarding RunMode

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).