Rendering/font size

Fonts have to be reinstalled in order to have a great font-size experience.
Run `CSSFontFormatter uninstallFonts` once - reinstallation should be triggered automatically on the next use of fonts.

Closes #99 
We do not return `nil`, but return a block that takes one argument and always returns `nil` to mimic the behaviour of a `parentResolver` with no values set if there is no `parentResolver`.