Tracking issue for current refactoring efforts

[regexident]

Environment:

• [x] Implementing let (or some kind of state for tests) (PR https://github.com/mackwic/rspec/pull/30)

Before & After

• [x] Implement before_all and after_all (PR https://github.com/mackwic/rspec/pull/30)
• [x] Real before_each and after_each (PR https://github.com/mackwic/rspec/pull/30)

Timing & Progress

• [ ] Formatter: Progress à la Fuubar
• [ ] Timing the tests (WIP)
• [x] Timing the test suite (WIP)

Filtering & Focussing

• [ ] Skipped tests and describes (experiment)
• [ ] Focused tests and describes (experiment)

Parallel & Async Tests

• [x] Parallel tests (probably via Rayon) (PR https://github.com/mackwic/rspec/pull/30)
• [ ] Async tests

Ergonomics

• [x] Simplify formatter instantiation and runner attachement? (PR https://github.com/mackwic/rspec/pull/30)
• [x] context::rdescribe should use the Simple formatter (PR https://github.com/mackwic/rspec/pull/30)
• [ ] Get rid of ctx in ctx.it() (experiment)

Integration

• [x] Integration with existing matcher crates
• [ ] Integration with rustc's test crate