This new feature can be accessed by invoking rustlings with --nocapture.
Both unit and integration tests added.
closes #262
BREAKING CHANGES:
The following function take a new boolean argument:
* `run`
* `verify`
* `test`
* `compile_and_test`
Hints are now accessible using the CLI subcommand `rustlings hint
<exercise name`.
BREAKING CHANGE: This fundamentally changes the way people interact with exercises.
BREAKING CHANGE: This changes the way you use `rustlings run` by now
requiring an abridged form of the previous filename, e.g:
`rustlings run exercises/if/if1.rs` becomes
`rustlings run if1`
