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`.
This was just more of a sanity check on my logic.  It should be `debug_assert!()`, but I was in thinking in C++.