Rustlings 4.0.0

See the changelog for what's changed.

The important breaking changes that make this a major release are:

• testX.rs files have been renamed quizX.rs, due to people confusing them with the similarly-named testsX.rs exercises (which are about testing, not being tested)
• You can now display the console output for tests using the new --nocapture option. This adds a new boolean argument to most CLI commands.

Thanks to all of the people who contributed! A full list can be seen here, there's too many people for me to manually list here, sorry 😓

To upgrade:

git fetch
git checkout tags/4.0.0