Show number of unread posts in feed selection
Use Python html2text instead of Rust version
Show which posts have already been read

Posts that are opened have their GUID stored in
$XDG_SHARE_HOME/roman/read-posts. For now, this filepath is
Linux-specific, but paths for other platforms will be added soon.
Remove unneeded import
Fix missing link to Rust website
Fix inconsistent spacing between sections
Sort feed list by alphabetical order
Use html2text to render post bodies
Revert to using a menu selector and add menu paging

There are still some edge cases that will break (for example, the pager
will break on lines that are longer than the terminal width), and the
instructions interface needs improvement, but this is sufficient for an
initial commit!
Simplify workflow of asking for user input
Add output paths to custom nimble build tasks
Fix capitalization error
Add Post and Feed types to handle user metadata
Improve leftover displayed options after interrupt
Add check for duplicate subscriptions
Remove useless function and error check
Show feed titles instead of URLs in selection menu
Ask user to select which feed to see posts from
Add ability to subscribe to feeds via --subscribe flag
Remove accidental double print of title