build(site): parse markdown into index and article with frontmatter

[rrvsh]

To do before merge:

• Make title, date, slug use fallbacks (should never be None)
• parse date into datetime or other data type that isnt string
• add Document.to_html to convert each field into html and return Html(String)
• load files into Vec
• resolve url path to look up date and slug in the vec and return document.to_html.into_response