update for rust 0.12.0-pre (or 0.11)

println was changed to the println!() macro, which is now reflected in
the code.

All Rust code, excluding chain_of_responsibility.rs (unimplemented) now
compiles on Rust

    rustc 0.12.0-pre

commit

    e178ebf681d532c1c965883ae34788713f748960