Style enhancements for header font and spacing between list items

[jefferythomas]

Here are a couple of enhancements that have been an issue while using MarkdownUI.

• Add a feature to provide more control over the font used for headers
• Add a feature to control the space between list items

[emartinson]

And also configure custom spacing per header level

[gonzalezreal]

Hi @jefferythomas and @emartinson,

Please take a look at the latest release: https://github.com/gonzalezreal/swift-markdown-ui/releases/tag/2.0.0

This version is a game-changer in terms of styling. You can do what you requested and much more.