Add reexport command

brood/src/commands/reexport.rs

@@ -0,0 +1,17 @@
+use std::fs::File;
+use std::io::{self, BufReader, BufWriter};
+use std::path::Path;
+
+use crate::data::AdjacencyList;
+
+pub fn reexport(from: &Path, to: &Path) -> io::Result<()> {
+    eprintln!(">> Import");
+    let from = BufReader::new(File::open(from)?);
+    let data = AdjacencyList::read(from)?;
+
+    eprintln!(">> Export");
+    let to = BufWriter::new(File::create(to)?);
+    data.write(to)?;
+
+    Ok(())
+}