16 bit Virtual Machine in Rust

Following Frank Stokes on YouTube, however, using Rust.

Also see TypeScript version.

Changes

1. Episode one. Implement MOV and ADD
2. Episode two. Extend MOV, implement JNE
3. Episode three. It is an instructional video on stack and stack frames, with no coding.
4. Episode four. Implement stack and stack frame, by adding PSH, POP, CAL, RET instructions.