* Fix #995 ICategoryChannel.CategoryID throws NotSupportedException

* Add tests

* change run mode of TestChannelCategories

* Add throw for GetCategoryAsync

* Add xml doc explaining why exception is thrown

* Add test coverage for text and voice channel categories

* initial implementation of INestedChannel

* more implementation of INestedChannel design

* Add case in RestChannel Create for Category type

* set the CategoryID for RestVoiceChannel

* rewrite channel category tests to work with existing pattern

* remove outdated todo

* Make IVoiceChannel implement INestedChannel

* remove redundant interface implementation

* Add c#7 feature from feedback

* Remove redundant GetCategoryAsync methods from socket entities

* Added configureawait to async methods

* change signature of interface GetCategoryAsync

* Add check for cachemode in rest channel GetCategory

* remove redundant IGuildChannel interface from ITextChannel and IVoiceChannel

- Because DocFX sucks at rendering langword

commit a85c5814a7
Author: Christopher F <computerizedtaco@gmail.com>
Date:   Sat Jan 6 22:25:48 2018 -0500

    Code cleanup

commit 4b243fd3dd
Author: Christopher F <computerizedtaco@gmail.com>
Date:   Sat Jan 6 22:08:28 2018 -0500

    Add support for channel categories (#907)

    commit 41ed9106f2
    Author: mrspits4ever <spits.lucas@gmail.com>
    Date:   Thu Dec 14 20:02:57 2017 +0100

        removed mentioning support for RestCategoryChannel, added channels property to SocketCategoryChannel

    commit 71142c3108
    Merge: 4589d731 678a7238
    Author: mrspits4ever <spits.lucas@gmail.com>
    Date:   Wed Dec 13 21:17:53 2017 +0100

        Merge branch 'dev' of https://github.com/RogueException/Discord.Net into feature/channel-categories

    commit 4589d73187
    Author: mrspits4ever <spits.lucas@gmail.com>
    Date:   Wed Dec 13 21:17:46 2017 +0100

        adressed requested changes

    commit d59b038efa
    Author: pegasy <pegasy@users.noreply.github.com>
    Date:   Mon Sep 25 18:53:23 2017 +0200

        Renamed classes / properties / methods to use CategoryChannel instead of ChannelCategory to be consistant with how text / voice channels are named.

    commit 5c4777dc8c
    Author: pegasy <pegasy@users.noreply.github.com>
    Date:   Sun Sep 24 19:08:25 2017 +0200

        removed Guild from class name for ChannelCategory
        Renamed all properties to use Category instead of Parent
        Throw exception on GetUsers / GetInvites etc for categories

    commit e18bd8c799
    Author: pegasy <pegasy@users.noreply.github.com>
    Date:   Sun Sep 24 15:49:51 2017 +0200

        Add support for channel categories (as its own channel type)

Resolves #859

* Partial fix of #810, addresses critical connection issues.

* Implement fix for REST.

* Implement fix on RestChannel.

Resolves #469