`rash` - A blazingly fast memory-safe POSIX shell

# Why?

I want to learn Rust and see how much effort I can put into making an interoperable software.

# Roadmap

- [x] Execute commands
- [x] Parse commands
- [ ] Variables
- [ ] Environment variables
- [ ] Builtins
  - [x] `cd`
  - [x] `:`
  - [ ] `set`
  - [ ] `alias`
  - [ ] `type`
- [ ] Command-line flags
- [ ] PS1
- [ ] Execute code from a file
- [ ] Clean error handling
- [ ] Override Ctrl-C