feat: migrate to ratatui (#26)

Co-authored-by: Ben PHL <benphawke@gmail.com>

examples/example.rs

@@ -6,13 +6,13 @@ use crossterm::{
     execute,
     terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
 };
-use std::{error::Error, io};
-use tui::{
+use ratatui::{
     backend::{Backend, CrosstermBackend},
     style::{Color, Modifier, Style},
     widgets::{Block, Borders},
     Terminal,
 };
+use std::{error::Error, io};
 
 use tui_tree_widget::{Tree, TreeItem};