Update to rust nightly. io => old_io

examples/main.rs

 extern crate serialize;
 extern crate tiled;
 
-use std::io::File;
-use std::io::BufferedReader;
+use std::old_io::{File, BufferedReader};
 use tiled::parse;
 
 fn main() {

src/lib.rs

@@ -4,7 +4,7 @@ extern crate flate2;
 extern crate xml;
 extern crate "rustc-serialize" as serialize;
 
-use std::io::{BufReader, IoError, EndOfFile};
+use std::old_io::{BufReader, IoError, EndOfFile};
 use std::str::FromStr;
 use std::collections::HashMap;
 use std::fmt;