report which lines changed on up/down

set_local_db, toggle_after_line and set_dot_env now return a
FileChange (path + before/after line pairs) instead of (), and main
prints it after each toggle so 'up'/'down' shows exactly what the
program rewrote in each env file.

src/main.rs

@@ -24,13 +24,13 @@ fn main() -> Result<()> {
     start_docker_compose(&config.container_service, &config.container_dir, start)?;
     if args.legacy {
         println!("[!] Legacy mode active.");
-        set_local_db(start, &config)?;
+        print!("{}", set_local_db(start, &config)?);
         toggle_index(start, &config)?;
     } else {
         println!("[!] Legacy mode deactivated.");
     }
 
-    set_dot_env(start, &config)?;
+    print!("{}", set_dot_env(start, &config)?);
 
     println!(
         "[!] Don't forget your interpreter! Project directory: {}",