Catch the first ligne of the config file

or throw a error !

src/main.rs

@@ -22,10 +22,12 @@ mod world;
 
 /// Parse the config file, generate the world and robot pool.
 fn parse_config(raw_conf: String, pool: &Vec<robot::Robot>) -> Result<world::World, &'static str> {
-    // test exemple, i am currently writting the real code.
-    // This function return the map OR an error inside a Result so we
-    // can catch error using '?' in main
-    // we also create robots here and put them into the pool.
+    let mut lines = raw_conf.lines();
+    // The first line of the config file should be the World.
+    let raw_map: &str = match lines.next() {
+        None => return Err("Could not read the first line of the config file !"),
+        Some(raw) => raw,
+    };
     Ok(world::World { x: 5, y: 5 })
 }