Instead of having to explain why
```rs
let mut x = 100;
let y = &mut x;
let mut z_owned = *y;
let z = &mut z_owned;
*y += 100;
*z += 1000;
```
and
```rs
let mut x = 100;
let y = &mut x;
let z = &mut *y;
*y += 100;
*z += 1000;
```
are different, you still get the point across about having only one mutable reference.
As it stands, this exercise does too much (dereferencing and having only one mutable reference), and by doing so confuses people.
Example of someone being confused by this:
<https://discord.com/channels/273534239310479360/273541522815713281/872689531428692040>
Improve the hints for move_semantics5, as well as the explanatory
comments in the code.
Previously, it was not clear what possible changes were allowed.
It seems that reordering the statements might be the intended solution.
The previous comment about not "adding newlines" doesn't make sense,
so treating it as "adding new lines" makes it more clear.
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.
