Rustlings 4.4.0

See the changelog for what's changed. Some highlights:

• A lot of small and large improvements to how exercises work
• rustlings list now displays structured data, and a takes a lot more options to filter that data:

• It also now shows you progress per-exercise, and a total summary of your completion:

• The compliation times for Rustlings should be significantly sped up, we replaced the crate we use for CLI option parsing with something more lightweight
• Rustlings now respects the NO_EMOJI envionment variable
• A new exercise, iterators5, has been added

To upgrade, run:

git fetch
git checkout tags/4.4.0