Add author meta tag

[sybrew]

Add an author meta tag that'll look like this:

<meta name="author" content="[Author name here]">

This tag is ambiguously described, but I gathered it should just state the post author's name.

LinkedIn is the only one that appears to make use of this.
They also recommend using it per their Post Inspector.

I do not know what the output of an embed will be like when it's added.
Testing is required. To get this going quickly, I've marked it for the next minor release.

Users may want to toggle it instead of having it always enabled. Still, we have already added similar data via Schema.org structured data.