Options to adjust title and subtitle size

[eteitelbaum]

For a .pdf document, I have noticed that if you have a longer title it looks too big with the default title settings. I know that you can adjust this with LaTeX code for font sizes like \large, \normalsize, or \small, but it might be more obvious/convenient for users if there were a YAML argument for adjusting the title and subtitle size like title-size: large.