* Fix potential nullref in embedBuilder value setter

* Null check on footer iconUrl

* Adding checks for the other URL properties

* Adding IsNullOrUri extension

* Setting StringExtensions as internal

* Add IUser#SendMessageAsync extension

* Add ConfigureAwait

* Removed GuildUserExtensions and moved the methods to IGuildUser and implementations

* Made changes per fox's suggestion: Change->Modify. New Modify overload.

* Oops

* Per Volt: reimplemented new endpoints

* Fixing broken docstrings

* I forgot that docstrings are XML

* Implemented atomic add/remove role endpoints

* Removed  so people aren't irked

* Added single-item role add/remove methods

Property can be renamed as needed.