Add support for F#.Formatting literate programming

[Krzysztof-Cieslak]

So this is adding support for F# Formatting literate programming feature discussed in #21

What should be implemented

• Loader loading fsx files and transforming them
• Port JS and CSS from F#.Formatting template (done partially, only for tooltips)
• Add download script link
• Use highlight JS styles for CSS classes assigned by F# Formatting
• Investigate using F# Formatting for markdown files instead of Markdig to have a single way of transforming markdown into html (check if F# Formatting supports features like tables)

Fixes #21

CC: @jbeeko

[jbeeko]

Re tables:

fsprojects/FSharp.Formatting#9

[Krzysztof-Cieslak]

This PR is now using F#.Formatting also for processing markdown files. Markdig is still used for API Reference comments due to reasons (MetadataGenerator API from F#.F is not exposing some of the options I need). Turns out, I was wrong.

[Krzysztof-Cieslak]

OK, this is ready - the link part is not done yet, I'll do it separate PR and in next version. But for now, this is already a huge improvement.