Add support for author meta in post content

[WiredUK]

I'd love to include the name of the author in the post if that is possible.

Currently, only [title], [excerpt], [permalink] and [tags] are supported, but [author] would be amazing to have for us.

Additionally, as a bonus, we also use the Co-Authors Plus plugin which allows us to assign multiple authors to posts so it would be amazing if we could also support this too, but that is far less useful.

Thanks!