Rust rewrite

edit: Rust port being worked on over at https://github.com/cjbassi/rtop. I plan to merge gotop PRs at least until rtop is feature equivalent, at which point I'll probably archive gotop.

Why rewrite in Rust?:

• I personally prefer working in Rust
• Rust is more difficult to learn but solves many of Go's shortcoming that I've encountered with gotop:
  • proper dependency management
  • generics
  • enforced thread safety
  • ability to embed files in the binary (colorschemes)
  • functional programming ergonomics
  • proper enums (enumerating keybinds, events, etc)
  • granular conditional compilation (not per file)
• there's a lot of awesome Rust packages gaining in maturity: tui-rs, crossterm, etc
  • will get truecolor colorschemes