Merge Johannes' changes into mine

I tried my best to merge Johannes' changes into what I have been working on.  The directory structure comes from running `cargo new 6502emu --bin`.  There is one unit test that can be compiled with `rustc --test -A dead_code 6502emu/src/main.rs`.
I think the module structure (for now) should be one main lib called 'emu6502', plus a corresponding executable, which I guess will contain test code for now. So exactly what you have, but split up.

I'm suggesting emu6502 instead of 6502emu because (I think) 6502emu can't be imported directly as a rust crate with the leading numeral.

The Cargo.toml for lib + exe is pretty simple--I'll make a pull request soon:

``` toml
[package]
name = "emu6502"
version = "0.0.1"
authors = ["The 6502-rs Developers"]

[lib]
# This will look in src/lib.rs
name = "emu6502"

[[bin]]
# This will look in src/bin/emu6502.rs
name = "emu6502"
```

See also http://crates.io/manifest.html#the-project-layout