Allow specifying a font style for a title on the title page

[AlexanderZobkov]

There is no way to define a font style for a title, for example bold or _bold italic_. Title string is always rendered with normal style. The same story with authors.

[mojavelinux]

This is possible. The keys are just missing from the theming guide. I'll mark it as a documentation issue.

[AlexanderZobkov]

Great, thanks! It looks like I overlooked these features when I was inspecting the sources.

[mojavelinux]

Would you like to update the theming guide?

[mojavelinux]

PR sent.

[AlexanderZobkov]

Looks OK. I think we can close the issue by meging the PR. Thanks for updating the theming guide,
Sorry, I didn't respond on the proposal to update the docs.

[mojavelinux]

Thanks for reviewing! You made me realize there were a few other things I wanted to fix, so I went ahead with the docs update.