[feat] Remove pandoc dependency

[jmetz]

Great project @theodore-s-beers :+1: !

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!