New API for easier value reading from stdin

Today reading value from stdin look like:

``` rust
let a: i32 = stdin.lock().lines().next().unwrap().unwrap().trim().parse().unwrap();
```

As i think, Rust needs easier way to do this. E. g. like:

``` rust
let a = stdin.read::<i32>().ok().expect("Write a number!");
let (b, c, d) = stdin.read::<(i32, f64, bool)>.ok().expect("Please, write integer, float and boolean!");
```
