* 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

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>

* Add request info to RateLimitedException

* Remove Promise from interface.

* Add Request to HttpException.

* Add API-level support for Rich Presences

* Add library-level support for Game presences

* Add model conversions for outgoing+incoming rich presences

* Refactored Game into Activities

* Integrated Activities with user entities

rebase hell from 5f3cb947a9

* Fix JSON converters for Activities

* Finish rebase, activity should be set on BaseSocketClient

* Use ApplicationId to define a rich presence

* Added SetActivityAsync to Base and Sharded Socket clients

* Remove public parameterless Game constructor

* Remove GameAssets, refactored to GameAsset

* Hide constructors for types that should be read-only

* Revert changes to Discord.Net.sln

got damned visual studio caching

* Refactor GameParty to use dedicated current/capacity values

Per feedback from @khionu

* Allow users to opt-in to proxies

* Allow opting in to proxies on the WebSocket

* Fix CreateGuildAsync not doing anything with the input stream for the guild icon.

Also fixes an issue with potential stream types that throw a NotSupportedException when checking its properties. [Apparently, they exist.](https://github.com/dotnet/corefx/blob/master/src/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpResponseStream.cs)

* Merged with old method

* Removed duplicate decl

* Add support for audit log reasons

* Made changes per discussion