Hints are now accessible using the CLI subcommand `rustlings hint
<exercise name`.
BREAKING CHANGE: This fundamentally changes the way people interact with exercises.
chore: Fix a couple broken book links
While I was fixing these, I figured maybe it's good to just use a consistent URL for book links: https://doc.rust-lang.org/book/
Is there a plan for what to do with this old 1.4.0 example that doesn't exist in the current version of the book? Perhaps at least include a disclaimer when recommending that folks check it out?
34e31232df/exercises/threads/README.md (L1)
Sub READMEs contain the relevant resources from the main
README of the web version. All second edition Rust Book links
were updated to the 2018 edition.
Fixed to typos in main README.md.
