The idea was proposed by eddyb in: rust-lang#31436 (comment)

Fix rust-lang#37116.

r? @jonathandturner

Start the lifetime section with an explanation of the issues that
lack of explicit lifetimes cause and how lifetimes alleviate these.

…uillaumeGomez

Changed error message E0408 to new format

Followed your text and was able to change the ouput to the new format.
I did not encounter any broken test therefore this is a really small commit.

Thanks for letting me hack on the compiler :)

r? @jonathandturner

Explain motivation behind lifetimes

Start the lifetime section with an explanation of the issues that lack of explicit lifetimes cause and how the explicit lifetimes solve these.

----------------

I had really hard time figuring out why I would need to care about the explicit reference lifetimes when going through the book at first. With strong background in C++, I'm familiar with the dangling reference problem - but given the section seems to focus more on the lifetime syntax and various ways to define lifetimes on functions and structs, I was unable to understand how they are used to solve the reference problem.

This PR is an attempt at getting the reader to understand what the explicit lifetimes are used for and why they are an awesome thing instead of a bit of syntax that just has to be written.

It's been less than a week that I've been diving into Rust so I'm far from certain about the terminology and technical correctness. I tried mimicking the existing terminology from the lifetimes section, but still no promises on getting it right.

Add missing urls for hash modules

r? @steveklabnik

…laumeGomez

rustdoc: color the question mark operator

The idea of coloring `?` specially was proposed by @eddyb in: rust-lang#31436 (comment)

…mcallister

add missing urls for BufWriter and BufReader

r? @steveklabnik

book: remove backticks in Type Aliases header

Fix rust-lang#37116.

run rustfmt on liblog

run rustfmt on libcore/num folder

Documented that RwLock might panic

Fixes rust-lang#37010

…ichton

add (missing) tar to list of packages to get under mingw

The distribution targets use tar, but the readme pacman invocation doesn't include the tar package.