Event handling (#5)

- Refactor `event` handling (heavily inspired by [crates-tui](https://github.com/ratatui/crates-tui/) via [Tui with Terminal and EventHandler](https://ratatui.rs/recipes/apps/terminal-and-event-handler/))
- Refactor widget structure
- Disable `nixos-unstable` temporarily
- Add `.rustfmt.toml`

src/terminal.rs

@@ -0,0 +1,22 @@
+use std::io::{stdout, Stdout};
+
+use color_eyre::eyre::Result;
+use crossterm::{execute, terminal::*};
+use ratatui::{backend::CrosstermBackend, Terminal as RatatuiTerminal};
+
+pub type Terminal = RatatuiTerminal<CrosstermBackend<Stdout>>;
+
+pub fn init() -> Result<Terminal> {
+    enable_raw_mode()?;
+    execute!(stdout(), EnterAlternateScreen)?;
+    let mut terminal = RatatuiTerminal::new(CrosstermBackend::new(stdout()))?;
+    terminal.clear()?;
+    terminal.hide_cursor()?;
+    Ok(terminal)
+}
+
+pub fn restore() -> Result<()> {
+    execute!(stdout(), LeaveAlternateScreen)?;
+    disable_raw_mode()?;
+    Ok(())
+}