Add CLI

- takes input-file, copies to output-file

src/main.rs

@@ -1,3 +1,27 @@
-fn main() {
-    println!("Hello, world!");
+use std::fs::File;
+use std::io::Write;
+
+use anyhow::{Context, Result};
+use structopt::StructOpt;
+
+#[derive(StructOpt)]
+struct Cli {
+    #[structopt(parse(from_os_str))]
+    input_file:  std::path::PathBuf,
+    #[structopt(parse(from_os_str))]
+    output_file: std::path::PathBuf,
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let args = Cli::from_args();
+
+    let content = std::fs::read_to_string(&args.input_file)
+        .with_context(|| format!("could not read source file {:?}", args.input_file))?;
+
+    let mut out = File::create(args.output_file)?;
+    out.write_all(&content.as_bytes())?;
+
+    out.sync_all()?;
+
+    Ok(())
 }