+ 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).

- As well as making minor adjustments here and there

- The link never worked in the first place and is rarely used.

* 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