Work in progress.

These changes were made a while back, and have since broken with newer
versions of Rust.  However, I'm committing them for now, since they may
be closer to the correct version; also to show what I was trying to do.
Adding updated binary-tree src.

Note: This does not compile, and will probably be removed yet.
I have upated it to remove syntax errors, but type checking still
doesn't pass.  This will probably need to be completely re-written.