Rustlings 4.6.0

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

• New exercises:
  • advanced_errs1 and advanced_errs2
  • modules3
• try_from_into and from_str have been reworked to include custom error types.
• Watch mode now has a quit and help command.
• Watch mode now also shows you a nice farewell message when you exit it.

To upgrade, run:

git fetch
git checkout tags/4.6.0