* 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* remove outdated todo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
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