[feat] Remove pandoc dependency

[jmetz]

Great project @theodore-s-beers 👍 !

One gripe though - having pandoc as a dependency (ie haskell and all the haskell libs used by pandoc) seems unnecessary, especially when rust-based alternatives exist like:

• https://gitlab.com/Kanedias/html2md
• https://github.com/nabbisen/mdka-rs
• https://github.com/letmutex/htmd
• https://github.com/wooorm/markdown-rs

[theodore-s-beers]

I'm open to this. htmd looks promising; I don't think it existed when I first wrote gloss. Will explore further. Thanks!

[theodore-s-beers]

I've now explored some of these libs. In fact, I quite like the API of htmd for turning HTML into Markdown. The problem is that I want the ultimate output to be in plain text, as it is now—and I've realized that Pandoc's plain text target is possibly the only one of its kind.