Rust book doesn't use deref coercions

I think deref coercions make life easier and they should be documented on the book. Currently, it seems like more-strings.md, pointers.md and unsafe.md could use this feature. Although I'm not sure where that should be told, maybe pointers.md?

Unrelated, old guides like guide-crates.md link to a nonexisting directory (src/doc/book) when they should actually point to src/doc/trpl

[steveklabnik]

Thanks @posixphreak ! In the future, feel free to make two issues for two unrelated things, so we can fix them in two patches if we need to.

[steveklabnik]

old guides like guide-crates.md link to a nonexisting directory (src/doc/book) when they should actually point to src/doc/trpl

This is not actually a bug, as they're for the generated output, not the in-tree source.