Refactored, and added Nix support

What did I do?

• Refactored the Haskell code. The code you had before was very repetitive... So, I made it dynamic and semi-easily configurable.
• Added nix support.
• Renamed byebye-exe to just byebye
• Tweaked the padding, it's cleaner now.
• Added a confirm feature (on by default)

What didn't I do?

• Modify the .org file.
  I don't use Emacs, so I figured I'd leave this up to you, I assume the process is simple, but I'm a vim user, so...
• Retain the original file paths.
  The file paths don't work on every system, but these work on mine... That should probably be rectified, but where should the icons be placed? Unsure...