A Minsky Machine in Rust's type system

See it in action with

cargo run --example subtract

Reference: http://goodmath.blogspot.com/2006/05/minsky-machine.html

Note that they use 1-based indexing where we use 0-based indexing

This was created in response to the challenge issued here: https://www.reddit.com/r/rust/comments/5y4x9r/challenge_rusts_type_system_is_not_turing_complete/

For an alternate proof that Rust's type system is Turing complete, see https://github.com/sdleffler/tarpit-rs