* 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.

* Initial Spotify support

* Remove GameAsset#ToEntity

- appId doesn't seem to be necessary, and Spotify Game doesn't return appId either.

* Implement SpotifyGame details

* Implement song Duration prop

* Add album art CDN

* Fix ActivityType

* Remove payload debug

* Add changes according to review

+ Make `ApplicationId` nullable
+ Move ctor after props

Previously it was implemented under Discord.Net.Rest, which seems
inconsistent and unnecessary.

This also allows Commands docstrings to reference EmbedBuilder, since
Commands only has a dependency on Core.

To reply with just a rich embed, users have to invoke ReplyAsync with
`ReplyAsync("", embed: embed)`, which seems wasteful, when they only
need to specify the embed.

In f19730e4, AddModule(s)Async was changed so that the IServiceProvider
was optional, both at compile time and runtime. This had the side effect
of meaning that there was no longer a compile-time hint that users would
need to pass an IServiceProvider to AddModulesAsync. I assumed this
would not be an issue - users would recognize the runtime exception here
and self correct - but activity in our Discord support channel would
indicate otherwise.

We now require the user to explicitly opt-out of dependency injection -
they are still free to pass null in place of an IServiceProvider if they
do not intend to use one, and the library will handle this at runtime.

* Move REST requests to appropiate class

* Add call to ClientHelper and expose to public API

* Expose shard count request in public api

* Expose method from interface

* Update sharded client to utilize the new method

* Method is already implemented in a base class

* Refactor name to fit pattern for methods returning a `Task`

* Adds missing ConfigureAwait

* Corrects unnecessary whitespace

* Removes unneeded whitespace

commit a8bafb90cd
Merge: f38dd4c4 7e04285e
Author: WamWooWam <wamwoowam@gmail.com>
Date:   Mon Mar 12 08:05:52 2018 +0000

    Merge branch 'dev' of https://github.com/WamWooWam/Discord.Net into dev

commit f38dd4c421
Author: WamWooWam <wamwoowam@gmail.com>
Date:   Mon Mar 12 08:05:49 2018 +0000

    Cleaned up & fixed code style.

commit 7e04285e5d
Author: Thomas May <wamwoowam@gmail.com>
Date:   Sun Mar 11 14:11:28 2018 +0000

    Revert changes to DefaultRestClient

    Didn't actually need to change this, whoops.

commit 3f5b2c8ef1
Author: WamWooWam <wamwoowam@gmail.com>
Date:   Sat Mar 10 19:30:44 2018 +0000

    Enabled embeds alongside uploaded files.

    God damn Discord is a mess.

Co-authored-by: WamWooWam <wamwoowam@gmail.com>