Add support for the keys "target" and "rel" in inline_attrs

[JonZeolla]

Describe the feature you'd like to request

I would like to be able to create a link that, when clicked, opens in a new tab.

I found that in the documentation, "only certain key-value attributes are supported for each syntax".

Describe the solution you'd like

I would like [here](example.md){target="_blank" rel="noreferer noopener"} to work.

Describe alternatives you've considered

My workaround is to directly use <a href="example.html" target="_blank" rel="noreferer noopener">