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.

* Added support for animated emoji

This was such a useful feature Discord, I'm glad you added this instead
of fixing bugs.

* Fix bugs in emote parser

* Added unit tests for emotes

* Add IEmbed#ToEmbedBuilder extension method

* Implementing reviewed changes.

* Switch to object initializers for author and footer.

* Add embed builder extensions

People in #dotnet_discord-net suggested that this should be part of
the lib after I demonstrated it

* Move some extensions into EmbedBuilder [2]

Apparently git didn't like that previous commit

* Fix error with EmbedBuilderExtensions

A summary of issues which happened:
- Git decided to add an amend commit (I told it to quit?)
- VS Code thinks everything is an error so it wasn't helpful
- dotnet decided to think there was no error until I deleted all
  build outputs and rebuild

Sometimes I question my ability to use version control properly.

Allows null embeds to be passed into ModifyAsync