Add Cli struct

src/cli.rs

@@ -0,0 +1,15 @@
+#[derive(Default)]
+pub struct Cli {
+    width: Option<usize>,
+    height: Option<usize>,
+}
+
+impl Cli {
+    pub fn new() -> Self {
+        Cli::default()
+    }
+
+    pub fn run(&mut self) -> Option<()> {
+        Some(())
+    }
+}

src/main.rs

@@ -1,3 +1,16 @@
-fn main() {
-    println!("Hello, world!");
+mod cli;
+
+use crate::cli::Cli;
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
+    match run() {
+        Some(_) => ExitCode::SUCCESS,
+        None => ExitCode::FAILURE,
+    }
+}
+
+fn run() -> Option<()> {
+    let mut cli = Cli::new();
+    cli.run()
 }